Zoom optical system, optical device and method for manufacturing the zoom optical system

ABSTRACT

A first lens group (G 1 ) having positive refractive power, a second lens group (G 2 ) having negative refractive power, a third lens group (G 3 ) having positive refractive power, a fourth lens group (G 4 ) having positive refractive power, a fifth lens group (G 5 ) are arranged in order from an object, and a distance between the first lens group (G 1 ) and the second lens group (G 2 ), a distance between the second lens group (G 2 ) and the third lens group (G 3 ), a distance between the third lens group (G 3 ) and the fourth lens group (G 4 ), and a distance between the fourth lens group (G 4 ) and the fifth lens group (G 5 ) change upon zooming, and a lens group arranged closest to an image is approximately fixed against an image surface (I) upon zooming, and the third lens group (G 3 ) moves along the optical axis upon focusing, and the following expression (1) is satisfied. 
         0.480   &lt;f   3   /ft&lt;   4.000    ( 1 )

TECHNICAL FIELD

The present invention relates to a zoom optical system, an opticaldevice and a method for manufacturing the zoom optical system.

TECHNICAL BACKGROUND

Conventionally, many zoom optical systems in which a lens group arrangedclosest to an object has positive refractive power are proposed as azoom optical system suitable for an interchangeable lens for a camera, adigital camera, a video camera, etc. (for example, refer to PatentDocument 1).

An optical system, in which focusing is performed by moving part of alens group along an optical axis, is proposed from among these zoomoptical systems.

Many methods for correcting image blur, in which an image is moved in adirection perpendicular to an optical axis by moving a lens group in thedirection perpendicular to the optical axis, are proposed.

PRIOR ART LIST Patent Document

-   [Patent Document 1] Japanese Laid-Open Patent Publication No.    H8-179214 (A)

SUMMARY OF THE INVENTION Means to Solve the Problems

A zoom optical system according to a first invention, comprises, inorder from an object, a first lens group having positive refractivepower, a second lens group having negative refractive power, a thirdlens group having positive refractive power, a fourth lens group havingpositive refractive power, and a fifth lens group, and a distancebetween the first lens group and the second lens group, a distancebetween the second lens group and the third lens group, a distancebetween the third lens group and the fourth lens group, and a distancebetween the fourth lens group and the fifth lens group change uponzooming, and a lens group arranged closest to an image is approximatelyfixed against an image surface upon zooming, and the third lens groupmoves along the optical axis upon focusing, and the followingconditional expression is satisfied.

4.80<f3/ft<4.000

where, ft denotes a focal length of the zoom optical system in atelephoto end state, and f3 denotes a focal length of the third lensgroup.

An optical device according to the first invention is equipped with thezoom optical system according to the first invention.

A method for manufacturing a zoom optical system according to the firstinvention, the zoom optical system comprises, in order from an object, afirst lens group having positive refractive power, a second lens grouphaving negative refractive power, a third lens group having positiverefractive power, a fourth lens group having positive refractive power,and a fifth lens group, and each lens is disposed in a lens-barrel sothat a distance between the first lens group and the second lens group,a distance between the second lens group and the third lens group, adistance between the third lens group and the fourth lens group, and adistance between the fourth lens group and the fifth lens group changeupon zooming, and a lens group arranged closest to an image is fixedagainst an image surface upon zooming, and the third lens group movesalong the optical axis upon focusing, and the following conditionalexpressions is satisfied.

0.480<f3/ft<4.000

wherein ft denotes a focal length of the zoom optical system in atelephoto end state, and

f3 denotes a focal length of the third lens group.

A zoom optical lens according to a second invention comprises, in orderfrom an object, a first lens group having positive refractive power, asecond lens group having negative refractive power, a third lens grouphaving positive refractive power, a fourth lens group having positiverefractive power, and a fifth lens group, and a distance between thefirst lens group and the second lens group, a distance between thesecond lens group and the third lens group, a distance between the thirdlens group and the fourth lens group, and a distance between the fourthlens group and the fifth lens group change upon zooming, and a lensgroup arranged closest to an image is approximately fixed against animage surface upon zooming, and the following conditional expressionsare satisfied.

0.480<f3/ft<4.000

−0.100<(d3t−d3w)/fw<0.330

where, ft denotes a focal length of the zoom optical system in atelephoto end state,

f3 denotes a focal length of the third lens group,

fw denotes a focal length of the zoom optical system in a wide-angle endstate,

d3w a distance on the optical axis from a lens surface arranged closestan image side of the third lens group in a wide-angle end state to alens surface arranged closest to an object side of the fourth lensgroup, and

d3t denotes a distance on the optical axis from a lens surface arrangedclosest to the image side of the third lens group in a telephoto endstate to a lens surface arranged closest to the object side of thefourth lens group.

An optical device according to the second invention is equipped with thezoom optical system according to the second invention.

A method for manufacturing a zoom optical system according to the secondinvention comprises, in order from an object, a first lens group havingpositive refractive power, a second lens group having negativerefractive power, a third lens group having positive refractive power, afourth lens group having positive refractive power, and a fifth lensgroup, and each lens is disposed in a lens-barrel so that a distancebetween the first lens group and the second lens group, a distancebetween the second lens group and the third lens group, a distancebetween the third lens group and the fourth lens group, and a distancebetween the fourth lens group and the fifth lens group changing uponzooming, and a lens group arranged closest to an image is approximatelyfixed to an image surface upon zooming, and the following conditionalexpressions are satisfied.

0.480<f3/ft<4.000

−0.100<(d3t−d3w)/fw<0.330

where, ft denotes a focal length of the zoom optical system in atelephoto end state,

f3 denotes a focal length of the third lens group,

fw denotes a focal length of the zoom optical system in a wide-angle endstate,

d3w denotes a distance on the optical axis from a lens surface arrangedclosest the image side of the third lens group in a wide-angle end stateto a lens surface arranged closest to the object side of the fourth lensgroup, and

d3t denotes a distance on the optical axis from a lens surface arrangedclosest to the image side of the third lens group in a telephoto endstate to a lens surface arranged closest to the object of the fourthlens group.

A zoom optical system according to a third invention comprises, in orderfrom an object, a first lens group having positive refractive power, asecond lens group having negative refractive power, a third lens grouphaving positive refractive power, a fourth lens group having positiverefractive power, and a fifth lens group, and a distance between thefirst lens group and the second lens group, a distance between thesecond lens group and the third lens group, a distance between the thirdlens group and the fourth lens group, and a distance between the fourthlens group and the fifth lens group change upon zooming, and a lensgroup arranged closest to an image is approximately fixed against animage surface upon zooming, and the fourth lens group comprises anaperture stop.

An optical device according to the third invention is equipped with thezoom optical system according to the third invention.

A method for manufacturing a zoom optical system according to the thirdinvention comprises, in order from an object, a first lens group havingpositive refractive power, a second lens group having negativerefractive power, a third lens group having positive refractive power, afourth lens group having positive refractive power, and a fifth lensgroup, and each lens is disposed in a lens-barrel so that a distancebetween the first lens group and the second lens group, a distancebetween the second lens group and the third lens group, a distancebetween the third lens group and the fourth lens group, and a distancebetween the fourth lens group and the fifth lens group change uponzooming, and a lens group arranged closest to an image is approximatelyfixed against an image surface upon zooming, and the fourth lens groupcomprises an aperture stop.

A zoom optical system according to a fourth invention comprises, inorder from an object, a first lens group having positive refractivepower, a second lens group having negative refractive power, a thirdlens group having positive refractive power, and a fourth lens grouphaving positive refractive power, and a distance between the first lensgroup and the second lens group, a distance between the second lensgroup and the third lens group, and a distance between the third lensgroup and the fourth lens group change upon zooming, and the fourth lensgroup comprises, in order from an object, a fourth A sublens groupmovable in a manner of having a component in a direction perpendicularto the optical axis in order to correct image blur and, and a fourth Bsublens group.

The optical device according to a fourth invention carries the zoomoptical system according to the fourth invention.

A method for manufacturing an zoom optical system according to a fourthinvention, the zoom optical system comprising, in order from an object,a first lens group having positive refractive power, a second lens grouphaving negative refractive power, a third lens group having positiverefractive power, and a fourth lens group having positive refractivepower, and each lens is disposed in a lens-barrel so that a distancebetween the first lens group and the second lens group, a distancebetween the second lens group and the third lens group, and a distancebetween the third lens group and the fourth lens group change uponzooming, and the fourth lens group comprises, in order from the object,a fourth A sublens group configured to enable to move in a manner ofhaving a component in a direction perpendicular to the optical axis inorder to correct image blur, and a fourth B sublens group.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates sectional views in a wide-angle end state (W),intermediate focal length state (M), and telephoto end state (T) of azoom optical system according to Example 1.

FIGS. 2A, 2B, and 2C respectively illustrate graphs showing variousaberrations upon focusing on an infinity object in a wide-angle endstate, intermediate focal length state, and telephoto end state of thezoom optical system according to Example 1.

FIGS. 3A, 3B, and 3C respectively illustrate graphs showing variousaberrations upon focusing on a short-distance object in a wide-angle endstate, intermediate focal length state, and telephoto end state (1.00 mof a distance between object images) of the zoom optical systemaccording to Example 1.

FIGS. 4A, 4B, and 4C respectively illustrate graphs showing meridionallateral aberration when correcting image blur upon focusing on aninfinity object in a wide-angle end state, intermediate focal lengthstate, and telephoto end state of the zoom optical system according toExample 1 (shift amount of a vibration-free lens group=0.1 mm).

FIG. 5 illustrates sectional views in a wide-angle end state(W),intermediate focal length state(M), and telephoto end state(T) of thezoom optical system according to Example 2.

FIGS. 6A, 6B, and 6C respectively illustrate graphs showing variousaberration upon focusing on an infinity object in a wide-angle endstate, intermediate focal length state, and telephoto end state of thezoom optical system according to Example 2.

FIGS. 7A, 7B, and 7C respectively illustrate graphs showing variousaberrations upon focusing a short-distance object in a wide-angle endstate, intermediate focal length state, and telephoto end state (1.00 mof a distance between object images) of the zoom optical systemaccording to Example 2.

FIGS. 8A, 8B, and 8C respectively illustrate meridional lateralaberration when correcting image blur upon focusing on an infinityobject in a wide-angle end state, intermediate focal length state, andtelephoto end state of the zoom optical system according to Example 2(shift amount of a vibration-free lens group=0.1 mm).

FIG. 9 illustrates sectional views in a wide-angle end state(W),intermediate focal length state(M), and telephoto end state(T) of thezoom optical system according to Example 3.

FIGS. 10A, 10B, and 10C respectively illustrate graphs showing variousaberrations upon focusing on an infinity object in a wide-angle endstate, intermediate focal length state, and telephoto end state of thezoom optical system according to Example 3.

FIGS. 11A, 11B, and 11C respectively illustrate graphs showing variousaberrations upon focusing on a short-distance object in a wide-angle endstate, intermediate focal length state, and telephoto end state of thezoom optical system according to Example 3 (1.00 m of a distance betweenimages).

FIGS. 12A, 12B, and 12C respectively illustrate graphs showingmeridional lateral aberration when correcting image blur upon focusingon an infinity object focusing in a wide-angle end state, intermediatefocal length state, and telephoto end state (shift amount of avibration-free lens group=0.1 mm) of the zoom optical system accordingto Example 3.

FIG. 13 illustrates sectional views in a wide-angle end state(W),intermediate focal length state(M), and telephoto end state(T) of thezoom optical system according to Example 4.

FIGS. 14A, 14B, and 14C respectively illustrate graphs showing variousaberrations upon focusing on an infinity object in a wide-angle endstate, intermediate focal length state, and telephoto end state of thezoom optical system according to Example 4.

FIGS. 15A, 15B, and 15C respectively illustrate graphs showing variousaberration upon focusing on a short-distance object focusing in awide-angle end state, intermediate focal length state, and telephoto endstate (1.00 m of a distance between object images) of the zoom opticalsystem according to Example 4.

FIGS. 16A, 16B, and 16C respectively illustrate meridional lateralaberration when correcting image blur upon focusing on an infinityobject in a wide-angle end state, intermediate focal length state, andtelephoto end state (shift amount of a vibration-free lens group=0.1 mm)of the zoom optical system according to Example 4.

FIG. 17 is a diagram illustrating a configuration of a camera comprisinga zoom optical system according to each of Examples 1 to 4.

FIG. 18 is a diagram illustrating an outline of a method manufacturing azoom optical system according to the first embodiment.

FIG. 19 is a diagram illustrating an outline of a method manufacturing azoom optical system according to the second embodiment.

FIG. 20 is a diagram illustrating an outline of a method formanufacturing a zoom optical system according to the third embodiment.

FIG. 21 is a diagram illustrating an outline of a method formanufacturing a zoom optical system according to the fourth embodiment.

DESCRIPTION OF THE EMBODIMENTS (FIRST TO FOURTH EMBODIMENTS)

A first embodiment will be now described with reference to the drawings.A zoom optical system ZL according to the first embodiment comprises, asillustrated in FIG. 1, in order from an object along an optical axis, afirst lens group G1 having positive refractive power, a second lensgroup G2 having negative refractive power, a third lens group G3 havingpositive refractive power, a fourth lens group G4 having positiverefractive power, and a fifth lens group G5, and a distance between thefirst lens group G1 and the second lens group G2, a distance between thesecond lens group G2 and the third lens group G3, a distance between thethird lens group G3 and the fourth lens group G4, and a distance betweenthe fourth lens group G4 and the fifth lens group G5 are configured tochange upon zooming. With this arrangement, it is possible to realizezooming, and suppress respective fluctuations of distortion accompanyingzooming, astigmatism, and spherical aberration.

The zoom optical system ZL according to the first embodiment isconfigured that a lens group arranged closest to an image (correspondingto the fifth lens group G5 in FIG. 1) is approximately fixed against animage surface I upon zooming. With this arrangement, it is possible tooptimize a change of a height of an off-axial flux of light passingthrough the lens group arranged closest to the image upon zooming, andsuppress a fluctuation of distortion or astigmatism. In addition, thisenables to simplify a lens-barrel structure configuring the zoom opticalsystem ZL according to the first embodiment, suppress decentering due tomanufacturing errors, etc., and suppress inclination of a surroundingimage surface and decentering coma aberration generated due todecentering of the lens group arranged closest to the image.

The zoom optical system ZL according to the first embodiment isconfigured that focusing is performed by moving the third lens group G3along the optical axis. With this arrangement, it is possible tosuppress a fluctuation of astigmatism and spherical aberration uponfocusing by suppressing amount of movement upon focusing on infinity,and suppressing a fluctuation of a height from the optical axisregarding light incident on the third lens group G3 which is a focusinglens group in a telephoto end state.

In the zoom optical system ZL according to the first embodiment, thefollowing conditional expression (1) is satisfied.

0.480<f3/ft<4.000   (1)

where, ft denotes a focal length of the zoom optical system ZL in atelephoto end state, and

f3 denotes a focal length of the third lens group G3.

The conditional expression (1) defines a range of an appropriate focallength of the third lens group G3. By satisfying the conditionalexpression (1), it is possible to suppress astigmatism and sphericalaberration upon zooming.

When a corresponding value of the conditional expression (1) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the third lensgroup G3 upon zooming, therefore high optical performance cannot berealized. When trying to suppress such aberration fluctuation, moreconfiguration lenses are needed, therefore downsizing is not possible.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable to set the lower limit of the conditionalexpression (1) to 0.570.

When the corresponding value of the conditional expression (1) exceedsan upper limit, a fluctuation of astigmatism generated in the fourthlens group G4 becomes excessive upon zooming, therefore high opticalperformance cannot be realized.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable that the upper limit of the conditionalexpression (1) is set to 0.3200. In order to additionally ensure theadvantageous effect of the first embodiment, it is preferable to set theupper limit of the conditional expression (1) to 2.400.

In the zoom optical system ZL according to the first embodiment, it ispreferable that the following conditional expression (2) is satisfied.

0.900<(−f2)/fw<1.800   (2)

where, fw denotes a focal length of the zoom optical system ZL in awide-angle end state, and

f2 denotes a focal length of the second lens group G2.

The conditional expression (2) defines a range of an appropriate focallength of the second lens group G2. By satisfying the conditionalexpression (2), it is possible to suppress a fluctuation astigmatism andspherical aberration upon zooming.

When a corresponding value of the conditional expression (2) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the second lensgroup G2 upon zooming, therefore high optical performance cannot berealized.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable to set the lower limit of the conditionalexpression (2) to 0.970. In order to additionally ensure theadvantageous effect of the first embodiment, it is preferable to set thelower limit of the conditional expression (2) to 1.065.

When a corresponding value of the conditional expression (2) exceeds anupper limit, it is necessary to enlarge, in order to secure apredetermined zoom ratio, a distance change between the first lens groupG1 and the second lens group G2 upon zooming. As a result, since a ratioof a diameter of an axial flux of light passing through the first lensgroup G1 and the second lens group G2 greatly changes, a fluctuation ofspherical aberration upon zooming becomes excessive, therefore highoptical performance cannot be realized.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable to set the upper limit of the conditionalexpression (2) to 1.600.

In the zoom optical system ZL according to the first embodiment, it ispreferable that the following conditional expression (3) is satisfied.

0.600<f3/f4<4.000   (3)

where, f4 denotes a focal length of the fourth lens group G4.

The conditional expression (3) defines a range of an appropriate focallength of the third lens group and the fourth lens group G4. Bysatisfying the conditional expression (3), it is possible to suppress afluctuation of astigmatism and spherical aberration upon focusing.

When a corresponding value of the conditional expression (3) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the third lensgroup G3 upon focusing, therefore high optical performance is notrealized.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable that the lower limit of the conditionalexpression (3) is set to 0.840. In order to additionally ensure theadvantageous effect of the first embodiment, it is preferable that thelower limit of a conditional expression (3) is set to 0.970.

When a corresponding value of the conditional expression (3) exceeds anupper limit, it is necessary to greatly change, in order to secure apredetermined focusing range, a distance between the third lens groupand the fourth lens group G4 upon focusing. As a result, since adiameter of an axial flux of light passing through the third lens groupgreatly changes, a fluctuation of spherical aberration upon focusingbecomes excessive, therefore high optical performance is not realized.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable to set the upper limit of the conditionalexpression (3) to 2.880.

In the zoom optical system ZL according to the first embodiment, it ispreferable that only the third lens group G3 moves along the opticalaxis upon focusing. With this arrangement, compared to a case in whichfocusing is performed with a plurality of lenses, it is possible tosuppress mutual decentering when manufacturing between focusing lensgroups upon focusing, and suppress generating decentering comaaberration, therefore high optical performance can be realized.

In the zoom optical system ZL according to the first embodiment, t ispreferable that the third lens group G3 is composed of one lenscomponent. With this arrangement, it is possible to downsize thefocusing lens groups, and suppress a fluctuation of spherical aberrationupon focusing. This configuration can contribute to speeding up uponfocusing.

In the zoom optical system ZL according to the first embodiment, it ispreferable that the third lens group G3 is composed of one single lens.With this arrangement, it is possible to downsize the focusing lensgroup. This configuration can contribute to speeding up upon focusing.Because lenses configuring the third lens group G3 are not composed of aplurality of and cementing lenses, it is possible to relatively suppressinfluence of decentering coma aberration, etc. due to decentering ofmutual lenses, therefore higher optical performance can be realized.

In the zoom optical system ZL according to the first embodiment, it ispreferable that the third lens group G3 comprises a lens made from anoptical material satisfying the following conditional expression (4).

48.00<v3   (4)

where, v3 denotes an Abbe number on the basis of d-line of the opticalmaterial used for the lens configuring the third lens group G3.

The conditional expression (4) defines a range of an appropriate Abbenumber of an optical material used for the lens configuring the thirdlens group G3. When a corresponding value of the conditional expression(4) becomes less than a lower limit, it becomes difficult to suppress afluctuation of chromatic aberration upon focusing, therefore highoptical performance cannot be realized.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable that the lower limit of the conditionalexpression (4) is set to 55.00. In order to additionally ensure theadvantageous effect of the first embodiment, it is preferable that thelower limit of a conditional expression (4) is set to 58.00.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable that the upper limit of a conditionalexpression (4) is set to 90.00. In order to further ensure theadvantageous effect of the first embodiment, it is preferable that theupper limit of a conditional expression (4) is set to 75.00.

In the zoom optical system ZL according to the first embodiment, it ispreferable that in the third lens group G3 at least one surface isaspherical-shaped. With this arrangement, it is possible to suppress afluctuation of astigmatism and spherical aberration upon zooming andfocusing.

In the zoom optical system ZL according to the first embodiment, it ispreferable that the following conditional expression (5) is satisfied.

−0.050<(d3t−d3w)/fw<0.330   (5)

where, fw denotes a focal length of the zoom optical system ZL in awide-angle end state,

d3w denotes a distance on the optical axis from a lens surface arrangedclosest to the image side of the third lens group G3 in a wide-angle endstate to a lens surface arranged closest to an object side of the fourthlens group G4, and

d3t denotes a distance on the optical axis from the lens surfacearranged closest to the image side of the third lens group G3 in atelephoto end state to the lens surface arranged closest to the objectside of the fourth lens group G4.

The conditional expression (5) defines an appropriate range of adistance change between the third lens group G3 and the fourth lensgroup G4 upon zooming. By satisfying the conditional expression (5), itis possible to suppress a fluctuation of astigmatism upon zooming.

When a corresponding value of the conditional expression (5) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism generated in the third lens group G3 upon zooming,therefore high optical performance cannot be realized.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable that the lower limit of a conditionalexpression (5) is set to 0.010.

When a corresponding value of the conditional expression (5) exceeds anupper limit, a change of height from the optical axis of an off-axialflux of light passing through the fourth lens group G4 upon zoomingbecomes large, therefore a fluctuation of astigmatism generated in thefourth lens group G4 becomes excessive, thereby high optical performancecannot be realized.

In order to further ensure the advantageous effect of the firstembodiment, it is appreciated that the upper limit of a conditionalexpression (5) is set to 0.275.

In the zoom optical system ZL according to the first embodiment, it ispreferable the fourth lens group G4 has an aperture stop S. With thisarrangement, it is possible to suppress a fluctuation of astigmatismgenerated in the fourth lens group G4, thereby high optical performancecan be realized.

In the zoom optical system ZL according to the first embodiment, it ispreferable that the aperture stop S is disposed between the third lensgroup G3 and the fourth lens group G4. With this arrangement, a changein a height direction from the optical axis of the off-axial flux oflight passing through the third lens group G3 and the fourth lens groupG4 upon zooming can be reduced, therefore a fluctuation of astigmatismgenerated in the third lens group G3 and the fourth lens group G4 can besuppressed, thereby high optical performance can be realized.

In the zoom optical system ZL according to the first embodiment, it ispreferable that the following conditional expression (6) is satisfied.

0.470<f4/ft<0.900   (6)

where, f4 denotes a focal length of the fourth lens group G4.

The conditional expression (6) defines a range of an appropriate focallength of the fourth lens group G4. By satisfying the conditionalexpression (6), it is possible to suppress a fluctuation of astigmatismand spherical aberration upon zooming.

When a corresponding value of the conditional expression (6) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the fourth lensgroup G4 upon zooming, therefore high optical performance cannot berealized.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable that the lower limit of the conditionalexpression (6) is set to 0.530.

When a corresponding value of the conditional expression (6) exceeds anupper limit, it is necessary to enlarge, in order to secure apredetermined zoom ratio, amount of movement of the fourth lens group G4against the image surface I upon zooming. As a result, since a diameterof an axial flux of light passing through the fourth lens group G4greatly changes, a fluctuation of the spherical aberration upon zoomingbecomes excessive, therefore high optical performance cannot berealized.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable that the upper limit of the conditionalexpression (6) is set to 0.720.

In the zoom optical system ZL according to the first embodiment, it ispreferable that a lens group arranged closest to the image has positiverefractive power. With this arrangement, magnification used in the lensarranged closest to the image becomes less than 100%, therefore it ispossible to relatively enlarge a composite focal length of the lensgroup arranged closer to the object (for example, corresponding to thefirst lens group G1 to the fourth lens group G4 in FIG. 1) rather thanthe lens group arranged closest to the image. As a result, it ispossible to relatively suppress influence of decentering comaaberration, etc. generated due to decentering between lenses, generatedin the lens arranged closer to the object side rather than the lensgroup arranged closest to the image when manufacturing, therefore highoptical performance can be realized.

In the zoom optical system ZL according to the first embodiment, it isappreciated that the following conditional expression (7) is satisfied.

3.000<fR/fw<9.500   (7)

where, fw denotes a focal length of the zoom optical system ZL in awide-angle end state, and

fR denotes a focal length of the lens group arranged closest to theimage.

The conditional expression (7) defines a range of an appropriate focallength of the lens group arranged closest to the image. By satisfyingthe conditional expression (7), it is possible to suppress a fluctuationof distortion and astigmatism upon zooming.

When a corresponding value of the conditional expression (7) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof distortion and astigmatism generated in the lens group arrangedclosest to the image upon zooming, therefore high optical performancecannot be realized.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable that the lower limit of the conditionalexpression (7) is set to 4.200.

When a corresponding value of the conditional expression (7) exceeds anupper limit, it becomes difficult to correct, by the lens group arrangedclosest to the image, a fluctuation of astigmatism generated in a lensgroup arranged closer to the object rather than the lens group arrangedclosest to the image, therefore high optical performance cannot berealized.

In order to further ensure the advantageous effect of the firstembodiment, it is preferable that the upper limit of the conditionalexpression (7) is set to 7.600.

In the zoom optical system ZL according to the first embodiment, it ispreferable that the lens group arranged closest to the image is thefifth lens group G5. With this arrangement, it is possible toappropriately correct a fluctuation of spherical aberration uponzooming.

In the zoom optical system ZL according to the first embodiment, thelens group arranged closest to the image can configure a sixth lensgroup G6. With this arrangement, it is possible to appropriately correcta fluctuation of astigmatism upon zooming.

In the zoom optical system ZL according to the first embodiment, it ispreferable that the third lens group G3 moves to an image side uponfocusing from an infinity object to a short-distance object. With thisarrangement, it is possible to focus only with the third lens group G3,and suppress a fluctuation of astigmatism and spherical aberration uponfocusing while downsizing the focusing lens group, therefore highoptical performance can be realized.

In the zoom optical system ZL according to the first embodiment, it ispreferable that the first lens group G1 moves to the object side uponzooming from a wide-angle end state to a telephoto end state. With thisarrangement, it is possible to suppress a change of a height from theoptical axis of the off-axial flux of light passing through the firstlens group G1 upon zooming. As a result, it is possible to suppress afluctuation of astigmatism upon zooming, generated in the first lensgroup G1. Note that the first lens group G1 may monotonically move tothe object side, or move in a manner of drawing a locus of a convex mayon the image side.

In the zoom optical system ZL according to the first embodiment, it ispreferable that a distance between the first lens group G1 and thesecond lens group G2 increases upon zooming from a wide-angle end stateto a telephoto end state. With this arrangement, since magnification ofthe second lens group G2 can be enlarged upon zooming from thewide-angle end state to the telephoto end state, a focal length of alllens groups can be configured to be long, therefore it is possible tosuppress a fluctuation of astigmatism and spherical aberration uponzooming.

In the zoom optical system ZL according to the first embodiment, it ispreferable that a distance between the second lens group G2 and thethird lens group G3 decreases upon zooming from a wide-angle end stateto a telephoto end state. With this arrangement, since compositemagnification up to the lens group arranged closest to the image fromthe third lens group G3 upon zooming from the wide-angle end state tothe telephoto end state, a focal length of all lens groups can beconfigured to be long, therefore it is possible to suppress afluctuation of astigmatism and spherical aberration upon zooming.

In the zoom optical system ZL according to the first embodiment, it ispreferable that the second lens group G2 moves to the object side uponzooming from a wide-angle end state to a telephoto end state. With thisarrangement, downsizing can be attained. Additionally, thisconfiguration enables to suppress a fluctuation of astigmatism andspherical aberration upon zooming. Note that the second lens group G2may monotonically move to the object side, or move in a manner ofdrawing a locus of a convex on the image side.

According to the zoom optical system ZL according to the firstembodiment equipped with the configurations above, it is possible torealize the zoom optical system having high optical performance uponzooming and focusing.

Next, referring of FIG. 17, a camera (optical device) equipped with theabove zoom optical system ZL is described. A camera 1 is, as shown inFIG. 17, a lens-interchangeable camera (so-called mirror-less camera)equipped with the above zoom optical system ZL as a photographing lens2. In this camera 1, light from an unillustrated object (photographicsubject) is condensed by the photographing lens 2, and configures aphotographic subject image on an imaging surface of an imaging unit 3via an unillustrated OLPF (Optical Low Pass Filter). A picture of thephotographic subject is created by photoelectrically converting thephotographic subject by a photoelectric conversion element provided inthe imaging unit 3. This picture is displayed on a EVF (Electronic ViewFinder) 4 provided in the camera 1. With this arrangement, it ispossible to observe the photographing subject via the EVF 4. When anunillustrated release button is pressed by a photographer, an image ofthe photographic subject taken by the imaging unit 3 is memorized in anunillustrated memory. Accordingly, the photographer can shoot thephotographic subject by the camera 1.

The zoom optical system ZL according to the first embodiment equippedwith in the camera 1 as the photographing lens 2 has, as found basedeach example mentioned below, high optical performance upon zooming andfocusing by means of characteristic lens configurations. Therefore,according to the camera 1 according to the first embodiment, an opticaldevice having high optical performance can be realized upon zooming andfocusing.

Note that in case of installing the above zoom optical system ZL on asingle-lens-reflex-type camera having a quick return mirror andobserving a photographic subject with a finder optical system, the sameadvantageous effect as the above camera 1 can be obtained. In case ofinstalling the zoom optical system ZL on a video camera, the sameadvantageous effect as the camera 1 can be obtained as well.

Next, referring to FIG. 18, a method for manufacturing the above zoomoptical system ZL will be outlined. Firstly, each lens is disposed in alens-barrel so that a first lens group G1 having positive refractivepower, a second lens group G2 having negative refractive power, a thirdlens group G3 having positive refractive power, a fourth lens group G4having positive refractive power, and a fifth lens group G5 are arrangedin order from an object (Step ST110). At this point, each lens isdisposed so that a distance between the first lens group G1 and thesecond lens group G2, a distance between the second lens group G2 andthe third lens group G3, a distance between the third lens group and thefourth lens group G4, and a distance between the fourth lens group G4and the fifth lens group G5 change upon zooming (Step ST120). Each lensis disposed so that a lens group arranged closest to the image isapproximately fixed against an image surface upon zooming (Step ST130).Each lens is disposed so that the third lens group moves along theoptical axis upon zooming (Step ST140). Each lens is arranged so that atleast a conditional expression (1) among the conditional expressions issatisfied (Step ST150).

0.480<f3/ft<4.000   (1)

where, ft denotes a focal length of the zoom optical system ZL in atelephoto end state, and

f3 denotes a focal length of the third lens group G3.

Exampling a lens arrangement according to the first embodiment, in thezoom optical system ZL illustrated in FIG. 1, as the first lens group G1having positive refractive power, a cemented lens composed of a negativemeniscus lens L11 having a concave surface facing the object and abiconvex positive lens L12, and a positive meniscus lens L13 having aconvex surface facing an object are disposed in a lens-barrel in orderfrom the object along the optical surface. As the second lens group G2having negative refractive power, a negative meniscus lens L21 having aconvex surface facing the object, a biconcave negative lens L22, and abiconvex positive lens L23 are disposed in the lens-barrel in order fromthe object along the optical axis. As the third lens group G3 havingpositive refractive power, a biconvex positive lens L31 is disposed inthe lens-barrel. As the fourth lens group G4 having positive refractivepower, a cemented lens composed of a negative meniscus lens L41 having aconvex surface facing the object and a biconvex positive lens L42, acemented lens composed of a biconvex positive lens L43 and a negativemeniscus lens L44 having a concave surface facing the object, and anegative meniscus lens L45 having a convex surface facing the object aredisposed in the lens-barrel in order from an object along the opticalaxis. As the fifth lens group G5, a positive meniscus lens L51 having aconcave surface facing the object is disposed in the lens-barrel. Eachlens is disposed in the lens-barrel so that the conditional expression(1) is satisfied (a corresponding value of the conditional expression(1) is 1.031).

According to the method for manufacturing the zoom optical systemaccording to the first embodiment, it is possible to manufacture thezoom optical system ZL having high optical performance upon zooming andfocusing.

As described above, according to the first embodiment, it is possible tosolve a problem owned by a conventional zoom optical system, such thatit is difficult to sufficiently maintain high optical performance uponfocusing.

Next, a second embodiment is described with reference to the drawings. Azoom optical system ZL according to the second embodiment comprises, asillustrated in FIG. 1, in order from the object along the optical axis,a first lens group G1 having positive refractive power, a second lensgroup G2 having negative refractive power, a third lens group havingpositive refractive power, a fourth lens group G4 having positiverefractive power, and a fifth lens group G5, wherein upon zooming, and adistance between the first lens group G1 and the second lens group G2, adistance between the second lens group G2 and the third lens group G3, adistance between the third lens group G3 and the fourth lens group G4,and a distance between the fourth lens group G4 and the fifth lens groupG5 are configured to change upon zooming. With this arrangement, it ispossible to suppress respective fluctuations such as distortionaccompanying zooming, astigmatism, and spherical aberration.

In the zoom optical system ZL according to the second embodiment, a lensgroup arranged closest to the image (corresponding to the fifth lensgroup G5 in FIG. 1) is approximately fixed against the image surface Iupon zooming. With this arrangement, a change of a height of the axialoutside flux of light passing through the lens group arranged closest tothe image is optimized upon zooming, therefore it is possible tosuppress a fluctuation of distortion and astigmatism. In addition, thisconfiguration enables to simplify a lens-barrel structure configuringthe zoom optical system ZL according to the second embodiment, andsuppress eccentricity due to manufacturing errors, etc., therefore it ispossible to suppress inclination of surrounding an image surface andeccentricity coma aberration generated in generated due to eccentricityof the lens group arranged closest to the image.

In the zoom optical system ZL according to the second embodiment thefollowing conditional expression (8) is satisfied.

0.480<f3/ft<4.000   (8)

where, ft denotes a focal length of the zoom optical system ZL in atelephoto end state, and

f3 denotes a focal length of the third lens group G3.

The conditional expression (8) defines a range of an appropriate focallength of the third lens group G3. By satisfying the conditionalexpression (8), it is possible to suppress a fluctuation of astigmatismand spherical aberration upon zooming.

When a corresponding value of the conditional expression (8) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the third lensgroup G3 upon zooming, thereby high optical performance cannot berealized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the lower limit of the conditionalexpression (8) is set to 0.570.

When a corresponding value of the conditional expression (8) exceedsupper limit, a fluctuation of astigmatism generated in the fourth lensgroup G4 becomes excessive upon zooming, therefore high opticalperformance cannot be realized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that set the upper limit of a conditionalexpression (8) is set to 3.200. In order to additionally ensure theadvantageous effect of the second embodiment, it is preferable that theupper limit of the conditional expression (8) si set to 2.400.

In the zoom optical system ZL according to the second embodiment thefollowing conditional expression (9) is satisfied.

−0.100<(d3t−d3w)/fw<0.330   (9)

where, fw denotes a focal length of the zoom optical system ZL in awide-angle end state,

d3w denotes a distance on the optical axis from a lens surface arrangedclosest to the image side of the third lens group G3 in the wide-angleend state to a lens surface arranged closest to the object side of thefourth lens group G4, and

d3t denotes a distance on the optical axis from the lens surfacearranged closest to the image side of the third lens group G3 in atelephoto end state to the lens surface arranged closest to the objectside of fourth lens group G4.

The conditional expression (9) defines an appropriate range the distancebetween the third lens group G3 and the fourth lens group G4 uponzooming. By satisfying the conditional expression (9), a fluctuation ofastigmatism upon zooming can be suppressed.

When a corresponding value of the conditional expression (9) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism generated in the third lens group G3 upon zooming,therefore high optical performance cannot be realized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the lower limit of the conditionalexpression (9) is set to −0.080.

When a corresponding value of the conditional expression (9) exceeds anupper limit, a change of a height from the optical axis of the axialflux of light passing through the fourth lens group G4 upon zoomingbecomes large, therefore a fluctuation of astigmatism generated in thefourth lens group G4 becomes excessive, thereby high optical performancecannot be realized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the upper limit of the conditionalexpression (9) is set to 0.275.

In the zoom optical system ZL according to the second embodiment, it ismost preferable that the lens group arranged closest to the image haspositive refractive power. With this arrangement, magnification used inthe lens group arranged closest to the image becomes less 100%,therefore a composite focal length of the lens group arranged closer tothe object than the lens group arranged closest to the image (forexample, corresponding to the first lens group G1 to the fourth lensgroup G4 in FIG. 1) can be relatively enlarged. As a result, it ispossible to relatively suppress influence of decentering comaaberration, etc. due to decentering of lenses generated in the lensgroup arranged closer to the object than the lens group arranged closestto the image when manufacturing, therefore high optical performance canbe realized.

In the zoom optical system ZL according to the second embodiment, it ispreferable that the following conditional expression (10) is satisfied.

3.000<fR/fw<9.500   (10)

where, fR denotes a focal length of the lens group arranged closest tothe image.

The conditional expression (10) defines a range of an appropriate focallength of the lens group arranged closest to the image. By satisfyingthe conditional expression (10), a fluctuation of distortion andastigmatism upon zooming can be suppressed.

When a corresponding value of the conditional expression (10) is lessthan a lower limit, it becomes difficult to suppress a fluctuation ofdistortion and astigmatism generated in the lens group arranged closestto the image upon zooming, thereby high optical performance is realized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the lower limit of the conditionalexpression (10) is set to 4.200.

When a corresponding value of the conditional expression (10) exceeds anupper limit, it becomes difficult to correct a fluctuation ofastigmatism generated in the lens group arranged closer to the objectside than the lens group arranged closest to the image, therefore highoptical performance cannot be realized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the upper limit of the conditionalexpression (10) is set to 7.600.

In the zoom optical system ZL according to the second embodiment, it ispreferable the following conditional expression (11) is satisfied.

0.730<(−f2)/fw<1.800   (11)

where, f2 denotes a focal length of the second lens group G2.

The conditional expression (11) defines a range of an appropriate focallength of the second lens group G2. By satisfying the conditionalexpression (11), a fluctuation of astigmatism and spherical aberrationupon zooming can be suppressed.

When a corresponding value of the conditional expression (11) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the second lensgroup G2 upon zooming, therefore high optical performance cannot berealized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the lower limit of the conditionalexpression (11) is set to 0.900. In order to additionally ensure theadvantageous effect of the second embodiment, it is preferable that thelower limit of the conditional expression (11) is set to 1.065.

When a corresponding value of the conditional expression (11) exceeds anupper limit, it is necessary to enlarge a distance between the firstlens group G1 and the second lens group G2 upon zooming in order tosecure a predetermined zoom ratio. As a result, since a ratio of adiameter of an axial flux of light passing through the first lens groupG1 and the second lens group G2 greatly changes, therefore a fluctuationof spherical aberration upon zooming becomes excessive, thereby highoptical performance cannot be realized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the upper limit of the conditionalexpression (11) is set to 1.600.

In the zoom optical system ZL according to the second embodiment, it ispreferable that the following conditional expression (12) is satisfied.

0.470<f4/ft<0.900   (12)

where, f4 denotes a focal length of the fourth lens group G4.

The conditional expression (12) defines a range of an appropriate focallength of the fourth lens group G4. By satisfying the conditionalexpression (12), a fluctuation of astigmatism and spherical aberrationupon zooming can be suppressed.

When a corresponding value of the conditional expression (12) is lessthan a lower limit, it becomes difficult to suppress a fluctuation ofastigmatism and spherical aberration generated in the fourth lens groupG4 upon zooming, therefore high optical performance cannot be realized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the lower limit of the conditionalexpression (12) is set to 0.530.

When a corresponding value of the conditional expression (12) exceeds anupper limit, it is necessary to enlarge amount of movement of the fourthlens group G4 against the image surface I upon zooming, in order tosecure a predetermined zoom ratio. As a result, since a diameter of theaxial flux of light passing through the fourth lens group G4 greatlychanges, a fluctuation of spherical aberration upon zooming becomesexcessive, therefore high optical performance cannot be realized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the upper limit of a conditionalexpression (12) is set to 0.720.

In the zoom optical system ZL according to the second embodiment, it ispreferable that the first lens group G1 moves to the object upon zoomingfrom a wide-angle end state to a telephoto end state. With thisarrangement, it is possible to suppress a height from the optical axisof the axial flux of light passing through the first lens group G1 uponzooming. As a result, it impossible to suppress a fluctuation ofastigmatism upon zooming generated in the first lens group G1.

In the zoom optical system ZL according to the second embodiment, it ispreferable that a distance between the first lens group G1 and thesecond lens group G2 increases upon zooming from a wide-angle end stateto a telephoto end state. With this arrangement, it is possible todouble magnification of the second lens group G2 upon zooming from awide-angle end state to a telephoto end state, therefore a focal lengthof all the lens groups can have a long configuration, therefore afluctuation of astigmatism and spherical aberration upon zooming can besuppressed.

In the zoom optical system ZL according to the second embodiment, it ispreferable that a distance between the second lens group G2 and thethird lens group G3 decreases upon zooming from a wide-angle end stateto a telephoto end state. With this arrangement, since a compositemagnification from the third lens group G3 to the fifth lens group G5can be doubled upon zooming from a wide-angle end state to a telephotoend state, a focal length of all lens groups can be configured to belong, therefore a fluctuation of astigmatism and spherical aberrationupon zooming can be suppressed.

In the zoom optical system ZL according to the second embodiment, it ispreferable that the following conditional expression (13) is satisfied.

0.350<(d1t−d1w)/ft<0.800   (13)

where, d1w denotes a distance on the optical axis from the lens surfacearranged closest to the image side of the first lens group G1 in awide-angle end state to the lens surface arranged closest to the objectside of the second lens group G2, and

d1t denotes a distance on the optical axis from the lens surfacearranged closest to the image side of the first lens group G1 in atelephoto end state to the lens surface arranged closest to the objectside of the second lens group G2.

The conditional expression (13) defines an appropriate range of a changeof a distance between the first lens group G1 and the second lens groupG2 upon zooming. By satisfying the conditional expression (13), afluctuation of coma aberration and astigmatism upon zooming can besuppressed.

When a corresponding value of the conditional expression (13) becomesless than a lower limit, it is necessary to improve refractive power ofthe first lens group G1 and the second lens group G2 in order to realizea predetermined zoom ratio. Then, it becomes difficult to suppress afluctuation of coma aberration and astigmatism upon zooming, generatedin the second lens group G2, therefore high optical performance cannotbe realized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the lower limit of the conditionalexpression (13) is set to 0.380.

When a corresponding value of the conditional expression (13) exceeds anupper limit, a change of a height from the optical axis of the axialflux of light passing through the first lens group G1 upon zoomingbecomes large, therefore a fluctuation of astigmatism generated in thefirst lens group G1 becomes excessive, thereby high optical performancecannot be realized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the upper limit of a conditionalexpression (13) is set to 0.650.

In the zoom optical system ZL according to the second embodiment, it ispreferable that the following conditional expression (14) is satisfied.

0.200<(d2w−d2t)/ft<0.700   (14)

where, d2w denotes a distance on the optical axis from the lens surfacearranged closest to the image side of the second lens group G2 in awide-angle end state to the lens surface arranged closest to the objectside of the third lens group G3, and

d2t denotes a distance on the optical axis from the lens surfacearranged closest to the image side of the second lens group G2 in atelephoto end state to the lens surface arranged closest to the objectto the third lens group G3.

The conditional expression (14) defines an appropriate range of a changeof a distance between the second lens group G2 and the third lens groupupon zooming. By satisfying the conditional expression (14), afluctuation of astigmatism and spherical aberration upon zooming can besuppressed.

When a corresponding value of the conditional expression (14) becomesless than a lower limit, it is necessary to improve refractive power ofthe second lens group G2 and the third lens group in order to realize apredetermined zoom ratio. Then, it becomes difficult to suppress afluctuation of astigmatism and spherical aberration upon zoominggenerated in the second lens group G2 and the third lens group G3,therefore high optical performance cannot be realized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the lower limit of the conditionalexpression (14) is set to 0.270.

When a corresponding value of the conditional expression (14) exceeds anupper limit, a change of a height from the optical axis of an off-axialflux of light passing through the second lens group G2 upon zoomingbecomes large, therefore a fluctuation of astigmatism generated in thesecond lens group G2 becomes excessive, thereby high optical performancecannot be realized.

In order to further ensure the advantageous effect of the secondembodiment, it is preferable that the upper limit of the conditionalexpression (14) is set to 0.550.

In the zoom optical system ZL according to the second embodiment, it ispreferable that the fourth lens group G4 has an aperture stop S. Withthis arrangement, it is possible to suppress a fluctuation ofastigmatism generated in the fourth lens group G4, therefore highoptical performance can be realized.

In the zoom optical system ZL according to the second embodiment, it ispreferable that the aperture stop S is disposed between the third lensgroup G3 and the fourth lens group G4. With this arrangement, a changeof a height from the optical axis of off-axis flux of light passingtough the third lens group G3 and the fourth lens group G4 upon zoomingcan be reduced, therefore a fluctuation of astigmatism generated in thethird lens group G3 and the fourth lens group G4 can be suppressed,thereby high optical performance can be realized.

In the zoom optical system ZL according to the second embodiment, it ispreferable that the third lens group G3 moves along the optical axisupon focusing. With this arrangement, amount of movement on a telephotoside upon focusing is suppressed, a fluctuation of the height from theoptical axis regarding light incident on the third lens group G3 whichis a focusing lens group on the telephoto side is suppressed, thereforea fluctuation of astigmatism and spherical aberration upon focusing canbe suppressed.

In the zoom optical system ZL according to the second embodiment, it ispreferable that the third lens group G3 moves to the image upon focusingfrom an infinity object to a short-distance object. With thisarrangement, it becomes possible to focus only with the third lens groupG3, a fluctuation of astigmatism and spherical aberration upon focusingcan be suppressed, therefore high optical performance can be realized.

According to the zoom optical system ZL according to the secondembodiment equipped with the above configuration, it is possible torealize the zoom optical system which has high optical performance overa whole zoom range.

Next, referring to FIG. 17, a camera (optical device) equipped with thezoom optical system ZL is described. This camera 1 has the sameconfigurations as those of the first embodiment, and its configurationshave already been described, the explanation is omitted here.

As found in each example mentioned below, the zoom optical system ZLaccording to the second embodiment equipped on the camera 1 as thephotographing lens 2 has high optical performance over the whole zoomrange. Thus, according to the camera 1 according to the secondembodiment, it is possible to realize an optical device has high opticalperformance over the whole zoom range.

Note that in case of installing the zoom optical system ZL mentionedabove on a single lens reflex type camera having a quick return mirrorand observing a photographic subject with a finder optical system, thesame advantageous effect as the above camera 1 can be obtained. In caseof installing the zoom optical system ZL on a video camera, the sameadvantageous effect as the camera 1 can be obtained.

Next, referring to FIG. 19, a method for manufacturing the zoom opticalsystem ZL is outlined. Firstly, each lens is disposed in a lens-barrelso that a first lens group having positive refractive power, a secondlens group having negative refractive power, a third lens group havingpositive refractive power, a fourth lens group having positiverefractive power, and a fifth lens group are arranged in order from anobject (Step ST210). At this point, each lens is disposed in thelens-barrel so that a distance between the first lens group G1 and thesecond lens group G2, a distance between the second lens group G2 andthe third lens group G3, a distance between the third lens group and thefourth lens group G4, and a distance between the fourth lens group G4and the fifth lens group G5 change upon zooming (Step ST220). Each lensis disposed so that the lens group arranged closest to the image isapproximately fixed against an image surface upon zooming (Step ST230).Each lens is arranged so that st least the conditional expressions (8)and (9) among the above conditional expressions are satisfied (StepST240).

0.480<f3/ft<4.000   (8)

31 0.100<(d3t−d3w)/fw<0.330   (9)

where, ft denotes a focal length of the zoom optical system ZL in atelephoto end state,

f3 denotes a focal length of the third lens group G3,

fw denotes a focal length of the zoom optical system ZL in a wide-angleend state,

d3w denotes a distance on the optical axis from a lens surface arrangedclosest to the image side of the third lens group G3 in a wide-angle endstate to a lens surface arranged closest to the object side of thefourth lens group G4, and d3t denotes a distance on the optical axisfrom the lens surface arranged closest to the image side of the thirdlens group G3 in a telephoto end state to the lens surface arrangedclosest to the object side of the fourth lens group G4.

Exampling a lens arrangement according to the second embodiment, in thezoom optical system ZL illustrated in FIG. 1, as the first lens group G1having positive refractive power, a cemented lens composed of a negativemeniscus lens L11 having a convex surface facing an object and abiconvex positive lens L12, and a positive meniscus lens L13 having aconvex surface facing the object are disposed in a lens-barrel, in orderfrom the object along the optical axis. As the second lens group G2having negative refractive power, a negative meniscus lens L21 having aconvex surface facing the object, a biconcave negative lens L22, and abiconvex positive lens L23 are disposed in the lens-barrel, in orderfrom the object along the optical axis. As the third lens group G3having positive refractive power, a biconvex positive lens L31 isdisposed in the lens-barrel. As the fourth lens group G4 having positiverefractive power, a cemented lens composed of a negative meniscus lensL41 having a convex surface facing the object and a biconvex positivelens L42, a cemented lens composed of a biconvex positive lens L43 and anegative meniscus lens L44 having a concave surface facing the object,and a negative meniscus lens L45 having a convex surface facing theobject are disposed in the lens-barrel, in order from the object alongthe optical axis. As the fifth lens group G5, a positive meniscus lensL51 having a concave surface facing the object is arranged in thelens-barrel. Each lens is disposed in the lens-barrel so that theconditional expressions (8) and (9) are satisfied (the correspondingvalue of the conditional expression (8) is 1.031, and the correspondingvalue of the conditional expression (9) is 0.215).

According to the method for manufacturing the zoom optical systemaccording to the second embodiment, it is possible to manufacture thezoom optical system ZL having high optical performance over the wholezoom range.

As described above, according to the second embodiment, it is possibleto solve a problem owned by a conventional zoom optical system such thatit is difficult to sufficiently maintain high optical performance over awhole zoom range upon focusing.

Next, a third embodiment is described with referred to drawings. Thezoom optical system ZL according to the third embodiment is configuredto comprise, as illustrated in FIG. 1, in order from an object along anoptical axis, a first lens group G1 having positive refractive power, asecond lens group G2 having negative refractive power, a third lensgroup G3 having positive refractive power, a fourth lens group G4 havingpositive refractive power, and a fifth lens group G5, and a distancebetween the first lens group G1 and the second lens group G2, a distancebetween the second lens group G2 and the third lens group G3, a distancebetween the third lens group G3 and the fourth lens group G4, and adistance between the fourth lens group G4 and the fifth lens group G5are configured to change upon zooming. With this arrangement, it ispossible to realize zooming, and suppress respective fluctuations ofspherical aberration, astigmatism, and distortion accompanying zooming.

In the zoom optical system ZL according to the third embodiment, thelens group arranged closest to the image (corresponding to the fifthlens group G5 in FIG. 1) is approximately fixed against the imagesurface I, upon zooming. With this arrangement, a change of a height ofthe axial flux of light passing through the lens group arranged closestto the image, upon zooming, is optimized, therefore a fluctuation ofastigmatism and distortion can be suppressed. In addition, thisconfiguration enables to simplify a lens-barrel structure configuringthe zoom optical system ZL according to the third embodiment, andsuppress eccentricity due to manufacturing errors, etc., therefore it ispossible to suppress inclination of surrounding an image surface andeccentricity coma aberration generated in generated due to eccentricityof the lens group arranged closest to the image.

In the zoom optical system ZL according to the third embodiment, thefourth lens group G4 is configured to comprise an aperture stop S. Withthis arrangement, it is possible to suppress a fluctuation ofastigmatism generated in the fourth lens group G4, therefore highoptical performance can be realized.

In the zoom optical system ZL according to the third embodiment, it ispreferable that the following conditional expression (15) is satisfied.

0.480<f3/ft<4.000   (15)

where, ft denotes a focal length of the zoom optical system ZL in atelephoto end state, and

f3 denotes a focal length of the third lens group G3.

The conditional expression (15) defines a range of an appropriate focallength of the third lens group G3. By satisfying the conditionalexpression (15), a fluctuation of astigmatism and spherical aberrationupon zooming can be suppressed.

When a corresponding value of the conditional expression (15) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the third lensgroup G3 upon zooming, therefore high optical performance can berealized.

In order to further ensure the advantageous effect of the thirdembodiment, it is preferable that the lower limit of the conditionalexpression (15) is set to 0.570.

When a corresponding value of the conditional expression (15) exceeds anupper limit, upon zooming, a fluctuation of astigmatism generated in thefourth lens group G4 becomes excessive, therefore high opticalperformance cannot be realized.

In order to further ensure the advantageous effect of the thirdembodiment, it is preferable that the upper limit of a conditionalexpression (15) is set to 3.200. In order to further ensure theadvantageous effect of the third embodiment, it is preferable that theupper limit of the conditional expression (15) is set to 2.400.

In the zoom optical system ZL according to the third embodiment, it ispreferable that the following conditional expression (16) is satisfied.

0.470<f4/ft<0.900   (16)

where, ft denotes a focal length of the zoom optical system ZL in atelephoto end state, and

f4 denotes a focal length of the fourth lens group G4.

The conditional expression (16) defines a range of an appropriate focallength of the fourth lens group G4. By satisfying the conditionalexpression (16), a fluctuation of astigmatism and aspherical aberrationupon zooming can be suppressed.

When a corresponding value of the conditional expression (16) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the fourth lensgroup G4 upon zooming, therefore high optical performance cannot berealized.

In order to further ensure the advantageous effect of the thirdembodiment, it is preferable that the lower limit of the conditionalexpression (16) is set to 0.530.

When a corresponding value of the conditional expression (16) exceeds anupper limit, it is necessary to enlarge amount of movement of the fourthlens group G4 to the image surface I upon zooming, in order to secure apredetermined zoom ratio. As a result, since a diameter of the axialflux of light passing through the fourth lens group G4 greatly changes,a fluctuation of spherical aberration upon zooming becomes excessive,therefore high optical performance cannot be realized.

In order to further ensure the advantageous effect of the thirdembodiment, it is preferable to set the upper limit of the conditionalexpression (16) to 0.720.

In the zoom optical system ZL according to the third embodiment, it ispreferable that the the lens group arranged closest to the image haspositive refractive power. With this arrangement, magnification used inthe lens group arranged closest to the image becomes less 100%,therefore a composite focal length of the lens group arranged closer tothe object side than the lens group arranged closest to the image (forexample, corresponding to the first lens group G1 to the fourth lensgroup G4 in FIG. 1) can be relatively enlarged. As a result, it ispossible to relatively suppress influence of decentering comaaberration, etc. due to decentering of lenses generated in the lensgroup arranged closer to the object than the lens group arranged closestto the image upon manufacture, therefore high optical performance can berealized.

In the zoom optical system ZL according to the third embodiment, it ispreferable that the following conditional expression (17) is satisfied.

3.000<fR/fw<9.500   (17)

where, fw denotes a focal length of the zoom optical system ZL in awide-angle end state, and

fR denotes a focal length of the lens group arranged closest to theimage.

The conditional expression (17) defines an appropriate focal length ofthe lens group arranged closest to the image. By satisfying theconditional expression (17), a fluctuation of distortion and astigmatismupon zooming can be suppressed.

When a corresponding value of the conditional expression (17) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof distortion and astigmatism generated in the lens group arrangedclosest to the image upon zooming, and high optical performance cannotbe realized.

In order to further ensure the advantageous effect of the thirdembodiment, it is preferable to set the lower limit of a conditionalexpression (17) to 4.200.

When a corresponding value of the conditional expression (17) exceeds anupper limit, it becomes difficult to correct a fluctuation ofastigmatism generated in the lens group arranged closer to the objectside than the lens group arranged closest to the image, therefore highoptical performance cannot be corrected.

In order to further ensure the advantageous effect of the thirdembodiment, it is preferable that the upper limit of the conditionalexpression (17) is set to 7.600.

In the zoom optical system ZL according to the third embodiment, it ispreferable that the following conditional expression (18) is satisfied.

0.730<(−f2)/fw<1.800   (18)

where, fw denotes a focal length of the zoom optical system ZL in awide-angle end state, and

f2 denotes a focal length of the second lens group G2.

The conditional expression (18) defines a range of an appropriate focallength of the second lens group G2. By satisfying the conditionalexpression (18), a fluctuation of astigmatism and spherical aberrationupon zooming can be suppressed.

When a corresponding value of the conditional expression (18) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the second lensgroup G2 upon zooming, therefore high optical performance cannot berealized.

In order to further ensure the advantageous effect of the thirdembodiment, it is preferable that the lower limit of the conditionalexpression (18) is set to 0.900. In order to further ensure theadvantageous effect of the third embodiment, it is preferable that thelower limit of the conditional expression (18) is set to 1.065.

When a corresponding value of the conditional expression (18) exceeds anupper limit, it is necessary to enlarge a change of a distance betweenthe first lens group G1 and the second lens group G2 upon zooming, inorder to secure a predetermined zoom ratio. As a result, since a ratioof a diameter of the axial flux of light passing through the first lensgroup G1 and the second lens group G2 greatly changes, a fluctuation ofspherical aberration upon zooming becomes excessive, therefore highoptical performance cannot be realized.

In order to further ensure the advantageous effect of the thirdembodiment, it is preferable that the upper limit of a conditionalexpression (18) is set to 1.600.

In the zoom optical system ZL according to the third embodiment, thefollowing conditional expression (19) is satisfied.

−0.100<(d3t−d3w)/fw<0.330   (19)

where, fw denotes a focal length of the zoom optical system ZL in awide-angle end state,

d3w denotes a distance on the optical axis from the lens arrangedclosest to the image side of the third lens group G3 in a wide-angle endstate to the lens surface arranged closest to the object

side of the fourth lens group G4, and d3t denotes a distance on theoptical axis from the lens surface arranged closest to the image side ofthe third lens group G3 in a telephoto end state to the lens arrangedclosest to the object side of the fourth lens group G4.

The conditional expression (19) defines an appropriate range of a changeof a distance between the third lens group G3 and the fourth lens groupG4 upon zooming. By satisfying the conditional expression (19), afluctuation of astigmatism upon zooming can be suppressed.

When a corresponding value of the conditional expression (19) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism generated in the third lens group G3 upon zooming,therefore high optical performance cannot be realized.

In order to further ensure the advantageous effect of the thirdembodiment, it is preferable that the lower limit of the conditionalexpression (19) is set to −0.080.

When a corresponding value of the conditional expression (19) exceeds anupper limit, a change a height from the optical axis of the off-axialflux of light passing through the fourth lens group G4 becomes largeupon zooming, therefore a fluctuation of astigmatism generated in thefourth lens group G4 becomes excessive, thereby high optical performancecannot be realized.

In order to further ensure the advantageous effect of the thirdembodiment, it is preferable that the upper limit of the conditionalexpression (19) is set to 0.275.

In the zoom optical system ZL according to the third embodiment, it ispreferable that the first lens group G1 moves to the object side uponzooming from a wide-angle end state to a telephoto end state. With thisarrangement, it is possible to suppress a change of a height on theoptical axis of the off-axial flux of light passing through the firstlens group G1 upon zooming. As a result, it is possible to suppress afluctuation of astigmatism generated in the first lens group G1 uponzooming.

In the zoom optical system ZL according to the third embodiment, it ispreferable that a distance between the first lens group G1 and thesecond lens group G2 increases upon zooming from a wide-angle end stateto a telephoto end state. With this arrangement, since magnification ofthe second lens group G2 can be doubled upon zooming from a wide-angleend state to a telephoto end state, a focal length of all lens groupscan be configured to be long, therefore a fluctuation of astigmatism andspherical aberration upon zooming can be suppressed.

In the zoom optical system ZL according to the third embodiment, it ispreferable that a distance between the second lens group G2 and thethird lens group G3 decreases upon zooming from a wide-angle end stateto a telephoto end state. With this arrangement, since a compositemagnification from the third lens group G3 to the fifth lens group G5upon zooming from a wide-angle end state to a telephoto end state, afocal length of all lens groups can be configured to be long, thereforea fluctuation of astigmatism and spherical aberration upon zooming canbe suppressed.

In the zoom optical system ZL according to the third embodiment, it ispreferable that an aperture stop S is disposed between the third lensgroup G3 and the fourth lens group G4. With this arrangement, a changeof a height from the optical axis of the off-axial flux of light passingthrough the third lens group G3 and the fourth lens group G4 uponzooming can be reduced, therefore a fluctuation of astigmatism generatedin the third lens group G3 and the fourth lens group G4 can besuppressed, thereby high optical performance can be realized.

In the zoom optical system ZL according to the third embodiment, it ispreferable that the third lens group G3 moves along the optical axisupon focusing. With this arrangement, amount of movement upon focusingon a telephoto side is suppressed, and a fluctuation of a height fromthe optical axis regarding light incident on the third lens group G3which is a focusing lens group on the telephoto side is suppressed,therefore a fluctuation of astigmatism and spherical aberration uponfocusing can be suppressed.

In the zoom optical system ZL according to the third embodiment, it ispreferable that the third lens group G3 moves to the image side uponfocusing from an infinity object to a short-distance object. With thisarrangement, focusing can be performed only with the third lens groupG3, therefore a fluctuation of astigmatism and spherical aberration uponfocusing can be suppressed, thereby high optical performance can berealized.

According to the zoom optical system ZL according to the thirdembodiment equipped with the above configurations, it is possible torealize the zoom optical system having high optical performance over thewhole zoom range.

Next, referring to FIG. 17, a camera (optical device) equipped with theabove zoom optical system ZL is described. This camera 1 has the sameconfigurations as those of the first embodiment, and its configurationsare already described, thus the explanations are omitted.

The zoom optical system ZL according to the third embodiment installedas the photographic lens 2 in the camera 1 has, as found in each examplementioned below, high optical performance over the whole zoom range withthe characteristic lens configurations. Thus, according to the camera 1according to the third embodiment, it is possible to realize an opticaldevice having high optical performance over the whole zoom range.

Note that in case of installing the zoom optical system ZL mentionedabove on a single lens reflex type camera having a quick return mirrorand observing a photographic subject with a finder optical system, thesame advantageous effect as the above camera 1 can be obtained. In caseof installing the zoom optical system ZL on a video camera, the sameadvantageous effect as the camera 1 can be obtained.

Next, referring to FIG. 20, a method for manufacturing the zoom opticalsystem ZL is outlined. Firstly, each lens is disposed in a lens-barrelso that a first lens group having positive refractive power, a secondlens group having negative refractive power, a third lens group havingpositive refractive power, a fourth lens group having positiverefractive power, and a fifth lens group are arranged in order from anobject (Step ST310). In this situation, each lens is disposed so that adistance between the first lens group G1 and the second lens group G2upon zooming, a distance between the second lens group G2 and the thirdlens group G3G, a distance between the third lens group G3 and thefourth lens group G4, and a distance between the fourth lens group G4and the fifth lens group G5 change upon zooming (Step ST320). Each lensis disposed so that the lens group arranged closest to the imagesapproximately fixed to an image surface upon zooming (Step ST330). Thefourth lens group G4 is configured to have an aperture stop S (StepST340).

Exampling a lens arrangement in the third embodiment, in the zoomoptical system ZL illustrated in FIG. 1, as the first lens group G1having positive refractive power, a cemented lens composed of a negativemeniscus lens L11 having a convex surface facing an object and abiconvex positive lens L12, and a positive meniscus lens L13 having aconvex surface facing an object are disposed in the lens-barrel in orderfrom an object along an optical axis. As the second lens group G2 havingnegative refractive power, a negative meniscus lens L21 having a convexsurface facing the object, a biconcave negative lens L22, and a biconvexpositive lens L23 are disposed in the lens-barrel in order from theobject along the optical axis. As the third lens group having positiverefractive power, a biconvex positive lens L31 is disposed in thelens-barrel. As the fourth lens group G4 having positive refractivepower, the aperture stop S, a cemented lens composed of a negativemeniscus lens L41 having a convex surface facing the object and abiconvex positive lens L42, a cemented lens composed of a biconvexpositive lens L43 and a negative meniscus lens L44 having a concavesurface facing to the object, and a negative meniscus lens L45 having aconvex surface facing the object are disposed in the lens-barrel. As thefifth lens group G5, a positive meniscus lens L51 having a concavesurface facing the object is disposed in the lens-barrel.

According to the method for manufacturing the zoom optical systemaccording to the third embodiment, it is possible to manufacture thezoom optical system ZL having high optical performance over the wholezoom range.

As described above, according to the third embodiment, it is possible tosolve a problem owned by the conventional zoom optical system such thatit is difficult to maintain sufficiently high optical performance overthe whole zoom range.

Next, the fourth embodiment is described with referred to drawings. Thezoom optical system ZL according to the fourth embodiment is configuredto comprise, as illustrated in FIG. 1, in order from an object along anoptical axis, a first lens group G1 having positive refractive power, asecond lens group G2 having negative refractive power, a third lensgroup G3 having positive refractive power, a fourth lens group G4 havingpositive refractive power, and a distance between the first lens groupG1 and the second lens group G2, a distance between the second lensgroup G2 and the third lens group G3, and a distance between the thirdlens group G3 and the fourth lens group G4 are configured to change uponzooming. With this arrangement, it is possible to realize zooming, andsuppress respective fluctuations of spherical aberration, astigmatism,and distortion accompanying zooming.

In the zoom optical system ZL according to the fourth embodiment, afourth lens group G4 comprises, in order from the object along theoptical axis, a fourth A sublens group G4A (vibration-free lens group)configured to enable to move in a manner of having a component in adirection perpendicular to the optical axis in order to correct imageblur, and a fourth B sublens group G4B. With this arrangement, a ratioof amount of movement regarding an image in the direction perpendicularto the optical axis against amount of movement of the fourth A sublensgroup G4A in the direction perpendicular to the optical axis can beappropriate, therefore astigmatism and decentering coma aberrationgenerated while the fourth A sublens group G4A is moving can besuppressed.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that a distance between the fourth A sublens group G4A andthe fourth B sublens group G4B is constant. With this arrangement, tiltdecentering between the fourth A sublens group G4A and the fourth Bsublens group G4B when manufacturing can be suppressed, thereforeastigmatism and decentering coma aberration due to the tilt decenteringcan be suppressed.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the following conditional expression (20) is satisfied.

0.480<f3/ft<4.000   (20)

where, ft denotes a focal length of the zoom optical system ZL in atelephoto end state, and

f3 denotes a focal length of the third lens group G3.

The conditional expression (20) defines a range of an appropriate focallength of the third lens group G3. By satisfying the conditionalexpression (20), it is possible to suppress a fluctuation of astigmatismand spherical aberration upon zooming, and astigmatism and decenteringcoma generated when the fourth A sublens group G4A is moving in thedirection perpendicular to the optical axis.

When a corresponding value of the conditional expression (20) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the third lensgroup G3 upon zooming, therefore high optical performance cannot berealized.

In order to further ensure the advantageous effect of the fourthembodiment, it is preferable that the lower limit of the conditionalexpression (20) is set to 0.570.

When a corresponding value of the conditional expression (20) exceeds anupper limit, a fluctuation of astigmatism generated in the fourth lensgroup G4 becomes excessive upon zooming, thereby high opticalperformance cannot be realized. A ratio of amount of movement regardingthe image in the direction perpendicular to the optical axis againstamount of movement in the direction perpendicular to the optical axisregarding the fourth A sublens group G4A decreases, accordinglynecessary amount of movement of the fourth A sublens group G4A in thedirection perpendicular to the optical axis increases. Then, it becomesimpossible to suppress astigmatism and decentering coma generated whenthe fourth A sublens group G4A is moving in the direction perpendicularto the optical axis

In order to further ensure the advantageous effect of the fourthembodiment, it is preferable that the upper limit of the conditionalexpression (20) is set to 3.200. In order to additionally ensure theadvantageous effect of the fourth embodiment, it is preferable that theupper limit of the conditional expression (20) is set to 2.400.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the fourth A sublens group G4A has positive refractivepower. With this arrangement, a ratio of amount of movement regardingthe image in the direction perpendicular to the optical axis againstamount of movement in the direction perpendicular to the optical axis ofthe fourth A sublens group G4A can be appropriate, thus astigmatism anddecentering coma aberration generated while the fourth A sublens groupG4A is moving can be suppressed.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the following conditional expression (21) is satisfied.

0.900<f4/fw<4.450   (21)

where, fw denotes a focal length of the zoom optical system ZL in awide-angle end state, and

f4 denotes a focal length of the fourth lens group G4.

The conditional expression (21) defines a range of an appropriate focallength of the fourth lens group G4. By satisfying the conditionalexpression (21), a fluctuation of astigmatism and spherical aberrationupon zooming can be suppressed.

When a corresponding value of the conditional expression (21) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the fourth lensgroup G4 upon zooming, thereby high optical performance cannot berealized.

In order to further ensure the advantageous effect of the fourthembodiment, it is preferable that the lower limit of the conditionalexpression (21) is set to 1.400. In order to additionally ensure theadvantageous effect of the fourth embodiment, it is preferable that thelower limit of the conditional expression (21) is set to 2.500.

When a corresponding value of the conditional expression (21) exceeds anupper limit, it is necessary to increase amount of movement regardingthe fourth lens group G4 against the image surface I, upon zooming, inorder to secure a predetermined zoom ratio. As a result, since adiameter of the axial flux of light passing through the fourth lensgroup G4 greatly changes, a fluctuation of spherical aberration uponzooming becomes excessive, therefore high optical performance cannot berealized.

In order to further ensure the advantageous effect of the fourthembodiment, it is preferable that the upper limit of the conditionalexpression (21) is set to 4.200.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the following conditional expression (22) is satisfied.

0.600<f3/f4<4.000   (22)

where, f3 denotes a focal length of the third lens group G3, and

f4 denotes a focal length of the fourth lens group G4.

The conditional expression (22) defines a range of an appropriate focallength of the third lens group G3 and the fourth lens group G4. Bysatisfying the conditional expression (22), it is possible to suppress afluctuation of astigmatism and spherical aberration upon zooming, andastigmatism and decentering coma aberration generated when the fourth Asublens group G4A is moving in the direction perpendicular to theoptical axis.

When a corresponding value of the conditional expression (22) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the third lensgroup G3 upon zooming, therefore high optical performance cannot berealized.

In order to further ensure the advantageous effect of the fourthembodiment, it is preferable that the lower limit of the conditionalexpression (22) is set to 0.840. In order to further ensure theadvantageous effect of the fourth embodiment, it is preferable that thelower limit of the conditional expression (22) is set to 0.970.

When a corresponding value of the conditional expression (22) exceeds anupper limit, a ratio of amount of movement regarding the image in thedirection perpendicular to the optical axis against amount of movementin the direction perpendicular to the optical axis of the fourth Asublens group G4A decreases, accordingly necessary amount of movementregarding the fourth A sublens group G4A in the direction perpendicularto the optical axis increases. Then, it is possible to suppressastigmatism and decentering coma aberration generated when the fourth Asublens group G4A moves in a direction perpendicular to the opticaldirection.

In order to further ensure the advantageous effect of the fourthembodiment, it is preferable that the upper limit of the conditionalexpression (22) is set to 2.880.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the following conditional expression (23) is satisfied.

0.155<(−f2)/ft<0.500   (23)

where, ft denotes a focal length of the zoom optical system ZL in atelephoto end state, and

f2 denotes a focal length of the second lens group G2.

The conditional expression (23) defines a range of an appropriate focallength of the second lens group G2. By satisfying the conditionalexpression (23), it is possible to suppress a fluctuation of astigmatismand spherical aberration upon zooming.

When a corresponding value of the conditional expression (23) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof astigmatism and spherical aberration generated in the second lensgroup G2 upon zooming, therefore high optical performance cannot berealized.

In order to further ensure the advantageous effect of the fourthembodiment, it is preferable that the lower limit of the conditionalexpression (23) is set to 0.170.

When a corresponding value of the conditional expression (23) exceeds anupper limit, it is necessary to enlarge a change of a distance betweenthe first lens group G1 and the second lens group G2 upon zooming inorder to secure a predetermined zoom ratio. As a result, since a ratioof a diameter of the axial flux of light passing through the first lensgroup G1 and the second lens group G2 greatly changes, a fluctuation ofspherical aberration upon zooming becomes excessive, therefore highoptical performance cannot be realized.

In order to further ensure the advantageous effect of the fourthembodiment, it is preferable that the upper limit of the conditionalexpression (23) is set to 0.380.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the following conditional expression (24) is satisfied.

0.750<f1/ft<3.000   (24)

where, ft denotes a focal length of the zoom optical system ZL in atelephoto end state, and

f1 denotes a focal length of the first lens group G1.

The conditional expression (24) defines a range of an appropriate focallength of the first lens group G1. By satisfying the conditionalexpression (24), it is possible to suppress a fluctuation of astigmatismand spherical aberration upon zooming.

When a corresponding value of the conditional expression (24) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof chromatic aberration of magnification, astigmatism, and sphericalaberration generated in the first lens group G1 upon zooming, thereforehigh optical performance is not realized.

In order to further ensure the advantageous effect of the fourthembodiment, it is preferable that the lower limit of the conditionalexpression (24) is set to 0.850.

When a corresponding value of the conditional expression (24) exceeds anupper limit, it is necessary to increase a change of a distance betweenthe first lens group G1 and the second lens group G2 upon zooming inorder to secure a predetermined zoom ratio. As a result, since a heightfrom the optical axis of the off-axial flux of light passing through thefirst lens group G1 greatly changes, a fluctuation of astigmatism uponzooming becomes excessive, therefore high optical performance cannot berealized.

In order to further ensure the advantageous effect of the fourthembodiment, it is preferable that the upper limit of the conditionalexpression (24) is set to 2.000. In order to additionally ensure theadvantageous effect of the fourth embodiment, it is preferable that theupper limit of the conditional expression (24) is set to 1.700.

It is preferable that the zoom optical system ZL according to the fourthembodiment comprise the fifth lens group G5 on an image side of thefourth lens group G4 along the optical axis, and a distance between thefourth lens group G4 and the fifth lens group G5 changes upon zooming.With this arrangement, since zooming can be efficiently performed,refractive power of the fourth lens group G4 can be weakened, thereforeit is possible to suppress a fluctuation of spherical aberration,astigmatism and distortion accompanying zooming and generated in thefourth lens group G4.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the lens group arranged closest to the image (forexample, corresponding to the fifth lens group G5 in FIG. 1) isapproximately fixed against the image surface I. By approximately fixingthe lens group arranged closest to the image against the image surface Imentioned above, a change of a height of the off-axial flux of lightpassing through the lens group arranged closest to the image can beoptimized, therefore a fluctuation of astigmatism and distortion can besuppressed. This enables to simplify a lens-barrel structure configuringthe zoom optical system ZL, suppress decentering due to manufacturingerrors, etc., and suppress inclination of surrounding image surfaces anddecentering coma aberration generated due to decentering of the lensgroup arranged closest to the image.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the lens group arranged closest to the image haspositive refractive power. With this arrangement, magnification used inthe lens arranged closest to the image becomes less than 100%, thereforeit is possible to relatively increase a composite focal length of thelens group arranged closer to the object (for example, corresponding tothe first lens group G1 to the fourth lens group G4 in FIG. 1) than thelens group arranged closest to the image. As a result, it is possible torelatively suppress influence of decentering coma aberration generateddue to decentering between lenses, generated in the lens arranged closerto the object than the lens group arranged closest to the image whenmanufacturing, therefore high optical performance can be realized.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the following conditional expression (25) is satisfied.

3.000<fR/fw<9.500   (25)

where, fw denotes a focal length of the zoom optical system ZL in awide-angle end state, and

fR denotes a focal length of the lens group arranged closest to theimage.

The conditional expression (25) defines a range of an appropriate focallength of the lens group arranged closest to the image. By satisfyingthe conditional expression (25), it is possible to suppress afluctuation of distortion and astigmatism upon zooming.

When a corresponding value of the conditional expression (25) becomesless than a lower limit, it becomes difficult to suppress a fluctuationof distortion and astigmatism generated in the lens group arrangedclosest to the image upon zooming, therefore high optical performancecannot be realized.

In order to further ensure the advantageous effect of the fourthembodiment, it is preferable that the lower limit of the conditionalexpression (25) is set to 4.200.

When a corresponding value of the conditional expression (25) exceeds anupper limit, it becomes difficult to correct a fluctuation ofastigmatism generated in the lens group arranged closer to the objectthan the lens group arranged closest to the image by the lens grouparranged closest to the image, therefore high optical performance cannotbe realized.

In order to further ensure the advantageous effect of the fourthembodiment, it is preferable that the upper limit of the conditionalexpression (25) is set to 7.600.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that only the third lens group G3 moves along the opticalaxis upon focusing. With this arrangement, amount of movement uponfocusing on a telephoto side is suppressed, and a fluctuation of aheight from the optical axis regarding light incident on the third lensgroup G3 which is a focusing lens group in the telephoto side can besuppressed, therefore a fluctuation of astigmatism and sphericalaberration upon focusing can be suppressed.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the third lens group G3 moves to the image side uponfocusing from an infinity object to a short-distance object. With thisarrangement, it becomes possible to focus only with the third lens groupG3, it is possible to suppress a fluctuation of astigmatism andspherical aberration upon focusing while downsizing the focusing lensgroup, therefore high optical performance can be realized.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the first lens group G1 moves to the object side uponzooming from a wide-angle end state to a telephoto end state. With thisarrangement, it is possible to suppress a change of a height from theoptical axis regarding an off-axial flux of light passing through thefirst lens group G1 upon zooming. With this arrangement, it is possibleto suppress a fluctuation of astigmatism upon zooming generated by thefirst lens group G1.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that a distance between the first lens group G1 and thesecond lens group G2 increases upon zooming from a wide-angle end stateto a telephoto end state. With this arrangement, since magnification ofthe second lens group G2 can be doubled upon zooming from the wide-angleend state to the telephoto end state, a focal length of all lens groupscan be configured to be long, therefore a fluctuation of astigmatism andspherical aberration upon zooming can be suppressed.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that a distance between the second lens group G2 and thethird lens group G3 decreases upon zooming from a wide-angle end stateto a telephoto end state. With this arrangement, since a compositemagnification regarding from the third lens group to the lens grouparranged closest to the image can increase upon zooming from thewide-angle end state to the telephoto end state, a focal length of alllens groups can be configured to be long, therefore a fluctuation ofastigmatism and spherical aberration upon zooming can be suppressed.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the fourth lens group G4 has an aperture stop S. Withthis arrangement, a fluctuation of astigmatism generated in the fourthlens group G4 can be suppressed upon zooming, therefore high opticalperformance can be realized.

In the zoom optical system ZL according to the fourth embodiment, it ispreferable that the aperture stop S is disposed between the third lensgroup G3 and the fourth lens group G4. With this arrangement, a changeof a height from the optical axis regarding an off-axial flux of lightpassing through the third lens group G3 and the fourth lens group G4upon zooming can be reduced, and a fluctuation of astigmatism generatedin the third lens group G3 and the fourth lens group G4 can besuppressed, therefore high optical performance can be realized.

According to the zoom optical system ZL according to the fourthembodiment equipped with the above configurations, it is possible torealize the zoom optical system not only having high optical performanceover a whole zoom range, but also having high optical performance highwhen correcting image blur.

Next, referring to FIG. 17, a camera (optical device) equipped with thezoom optical system ZL is described. This camera 1 has the sameconfigurations as those of the first embodiment, and its configurationshave already been described, the explanation is omitted here.

As found in each example mentioned below, the zoom optical system ZLaccording to the fourth embodiment equipped on the camera 1 as thephotographing lens 2 has not only high optical performance over thewhole zoom range, by the characteristic lens configurations, but alsohave high optical performance when correcting image blur. Therefore,according to the camera 1 according to the fourth embodiment, it ispossible to realize an optical device not only having high opticalperformance over the whole zoom range, but also having high opticalperformance when correcting image blur.

Note that in case of installing the zoom optical system ZL mentionedabove on a single lens reflex type camera having a quick return mirrorand observing a photographic subject with a finder optical system, thesame advantageous effect as the above camera 1 can be obtained. In caseof installing the zoom optical system ZL on a video camera, the sameadvantageous effect as the camera 1 can be obtained.

Next, referring to FIG. 21, a method for manufacturing the zoom opticalsystem ZL is outlined. Firstly, each lens is disposed in a lens-barrelso that a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, a third lens grouphaving positive refractive power, and a fourth lens group G4 havingpositive refractive power are arranged in order from an object (StepST410). At this point, each lens is disposed so that a distance betweenthe first lens group G1 and the second lens group G2, a distance betweenthe second lens group G2 and the third lens group G3, and a distancebetween the third lens group G3 and the fourth lens group G4 change uponzooming (Step ST420). Each lens is disposed so that the fourth lensgroup G4 comprises, in order from an object, a fourth A sublens groupG4A configured to enable to move in a manner of having a component in adirection perpendicular to the optical axis in order to correct imageblur, and a fourth B sublens group G4B (Step ST430).

Exampling a lens arrangement according to the fourth embodiment, thezoom optical system ZL illustrated in FIG. 1, as the first lens group G1having positive refractive power, a cemented lens composed of a negativemeniscus lens L11 having a convex surface facing the object and abiconvex positive lens L12, and a positive meniscus lens L13 having aconvex surface facing the object are disposed in the lens-barrel. As thesecond lens group G2 having negative refractive power, a negativemeniscus lens L21 having a convex surface facing the object, a biconcavenegative lens L22, and a biconvex positive lens L23 are disposed in thelens-barrel. As the third lens group G3 having positive refractivepower, a biconvex positive lens L31 is disposed in the lens-barrel. Asthe fourth lens group G4 having positive refractive power, a fourth Asublens group G4A configured of a cemented lens composed of a negativemeniscus lens L41 having a convex surface facing the object and abiconvex positive lens L42, a fourth B lens group G4B composed of acemented lens composed of a biconvex positive lens L43 and a negativemeniscus lens L44 having a concave surface facing the object, and anegative meniscus lens L45 having a convex surface facing the object aredisposed in the lens-barrel in order from the object along the opticalaxis. As the fifth lens group G5, a positive meniscus lens L51 having aconcave surface facing the object is disposed in the lens-barrel.

According to the method for manufacturing the zoom optical systemaccording to the fourth embodiment, it is possible to manufacture thezoom optical system ZL not only having high optical performance over thewhole zoom range, but also having high optical performance whencorrecting image blur.

As described above, according to the fourth embodiment, it is possibleto solve a problem such that it is difficult to maintainsufficiently-high optical performance over the whole zoom range, and aproblem such that it is difficult to obtain sufficiently-high opticalperformance when correcting image blur, owned by a conventional zoomoptical system.

Examples According to First to Fourth Embodiments

Each example according to the first to fourth embodiments is describedbased on drawings. Tables 1 to 4 are now shown, and these are Tables ofeach various data according to Example 1 to Example 4.

However, Example 4 corresponds only to the fourth embodiment.

Each reference sign regarding FIG. 1 according to Example 1 is usedindependently for every example, in order to avoid complicatingexplanations due to swelling of the digit number of reference signs.Therefore, even if attached with the same reference signs as those indrawings according to other examples, this does not necessarily mean thesame configurations as those in the other examples.

In each example, d-line (wave length of 587.5620 nm) and g-line (wavelength of 435.8350 nm) are selected as subjects for calculatingaberration characteristics.

In the [Lens data] in tables, a surface number means an order of eachoptical surface from the object side along a direction light travels, Rmeans a radius of curvature of each optical surface, D means a surfacedistance on the optical axis from each optical surface to the nextoptical surface (or image surface), nd means a refractive index againstd-line of a material of a optical member, and vd means an Abbe number onthe basis of d-line of a material of the light member. Object surfacemeans an object surface, (Variable) means a variable distance betweensurfaces, “∞” of a radius of curvature means a plane or an aperture,(Stop S) means an aperture stop S, and an image surface means an imagesurface I. The refractive index “1.000000” of air is omitted. In a casethe optical surface is an aspherical surface, a sign “*” is assigned tothe surface number and a paraxial radius of curvature is shown in acolumn of a radius of curvature R.

In [Aspherical surface data] in tables, regarding the asphericalsurfaces in the [Lens data], the configuration is defined by thefollowing expression (a). X(y) means a distance along the optical axisdirection from a tangent plane in a vertex of the aspherical surface toa position on the aspherical surface in height y, and R means a radiusof curvature (paraxial radius of curvature) of a criterion sphericalsurface, κ means a conic constant, and, Ai means an i-th asphericalsurface coefficient. “E−n” means “×10^(−n).” For example,1.234E−05=1.234×10⁻⁵. Note that the secondary aspherical surfacecoefficient A2 is 0, and its description is omitted.

x(y)=(y ² /R)/{1+(1−_(k) ×y ² /R ²)^(1/2) }+A4y ⁴ +A6y ⁶ +A8y ⁸ +A10y ¹⁰+A12y ¹²   (a)

In [Various data] in Tables, f means a focal length of a lens wholesystem, and FNo means a F number, ca means an half-angle of view (units:degree), Y means an image height, φ means the diameter of the aperturestop S, TL means a total optical length of a lens (a distance on theoptical axis from a first surface upon focusing on an infinity object tothe image surface I), and BF means backfocus (a distance on the opticalaxis from the lens surface arranged closest to the image surface uponfocusing on the infinity object to the image surface I). W means awide-angle end state, M means an intermediate focal length state, and Tmeans a telephoto end state.

In [Variable distance data] in Tables, a value Di of a variable distancein each state of a wide-angle end state upon focusing on infinity (W),an intermediate focal length state (M), and a telephoto end state (T)are shown. Note that Di means a variable distance between an i-thsurface and an (i+1)-th surface.

In [Amount of movement of focusing group upon focusing] in Tables,amount of movement of a focusing lens group (the third lens group G3)from an infinity focusing state to a short-distance focusing state(distance between object images: 1.00 m) is shown. Here, regarding amoving direction of the focusing lens group, moving to the image side isdefined as positive. An shooting distance means a distance from theobject to the image surface I.

In [lens group data] in Tables, a frontend surface and a focal lengthregarding each lens group are shown.

In [Values corresponding to the conditional expressions] in Tables,values corresponding to the above conditional expressions are shown.

Hereinafter, in all general data values, regarding the focal length f, aradius of curvature R, a distance D, and other lengths, etc. as shown,“mm” is generally used except a specific request, however an opticalsystem is not limited to the above, since equivalent optical performancecan be obtained even if the optical system is proportionally enlarged orproportionally shrinked. Moreover, the unit is not limited to “mm, ”another appropriate unit is available, instead.

The explanations concerning the tables are common among all theexamples, thus hereinafter the explanation is omitted.

EXAMPLE 1

Example 1 is described using FIG. 1, FIGS. 2A, 2B and 2C, FIGS. 3A, 3Band 3C, FIGS.4A, 4B and 4C and Table 1. The zoom optical system ZL (ZL1)according to Example 1 comprises, as illustrated in FIG. 1, in orderfrom an object along an optical axis, a first lens group G1 havingpositive refractive power, a second lens group G2 having negativerefractive power, a third lens group G3 having positive refractivepower, a fourth lens group G4 having positive refractive power, and afifth lens group G5 having positive refractive power. An aperture stop Sis provided between the third lens group G3 and the fourth lens groupG4, and the aperture stop S configures the fourth lens group G4. Thefifth lens group G5 is the lens group arranged closest to the image.

The first lens group G1 is composed of, in order from the object alongthe optical axis, a cemented lens composed of a negative meniscus lensL11 having a convex surface facing the object and a biconvex positivelens L12, and a positive meniscus lens L13 having a convex surfacefacing the object.

The second lens group G2 is composed of, in order from the object alongthe optical axis, a negative meniscus lens L21 having a convex surfacefacing the object, a biconcave negative meniscus lens L22, and abiconvex positive lens L23. Note that the negative meniscus lens L21 isa complexed aspherical lens made from resin and glass, in which a lenssurface on the object side is aspherical shaped.

The third lens group G3 is composed of a biconvex positive lens L31.Note that the positive lens L31 is a glass-molded aspherical lens, inwhich lens surfaces on the object and image sides are aspherical shaped.

The fourth lens group G4 is composed of, in order from the object alongthe optical axis, a fourth A sublens group G4A configured of a cementedlens composed of a negative meniscus lens L41 having a convex surfacefacing the object and a biconvex positive lens L42, a fourth B sublensgroup G4B configured of a cemented lens composed of a biconvex positivelens L43 and a negative meniscus lens L44 having a concave surfacefacing the object, and a negative meniscus lens L45 having a convexsurface facing the object. Note that the negative meniscus lens L44 is aglass-molded aspherical lens in which a lens surface on the image sideis aspherical shaped.

The fifth lens group G5 is composed of a positive meniscus lens L51having a concave surface facing the object.

In the zoom optical system ZL1 according to the present example, thefirst lens group G1 to the fourth lens group G4 moves along the opticalaxis so that an air distance between the first lens group G1 and thesecond lens group G2, an air distance between the second lens group G2and the third lens group G3, an air distance between the third lensgroup G3 and the fourth lens group G4, and an air distance between thefourth lens group G4 and the fifth lens group G5 respectively changeupon focusing from a wide-angle end state to a telephoto end state. Thefifth lens group G5 is fixed to the image surface I.

Specifically speaking, the first lens group G1 to the fourth lens groupG4 move to the object side. The aperture stop S moves to the object sidetogether with the fourth lens group G4.

With this arrangement, upon zooming, the air distance between the firstlens group G1 and the second lens group G2 increases, the air distancebetween the second lens group G2 and the third lens group decreases, theair distance between the third lens group G3 and the fourth lens groupG4 increases, and the air distance between the fourth lens group G4 andthe fifth lens group G5 increase. The air distance between the aperturestop S and the third lens group G3 increases.

Focusing is performed by moving the third lens group G3 along theoptical axis. Specifically speaking, this is performed by moving thethird lens group G3 to the image side along the optical axis uponfocusing from an infinity object to a short-distance object.

When image blur is generated, image blur on the image surface I iscorrected (vibration-controlled) by moving the fourth A sublens groupG4A as a vibration-free lens group in a manner of having a component ina direction perpendicular to the optical axis.

Table 1 shows values of each various data in Example 1. Surface numbers1 to 25 in Table 1 correspond to each optical surface of ml to m25illustrated in FIG. 1.

TABLE 1 [Lens Data] Surface number R D nd νd Object ∞ surface 1 132.72111.6000 1.846660 23.80 2 54.2419 4.5271 1.589130 61.22 3 −1401.49210.1000 4 36.9475 4.0173 1.696800 55.52 5 200.3945 D5 (Variable) *6510.0000 0.0800 1.560930 36.64 7 288.8364 1.0000 1.816000 46.59 8 8.86764.8531 9 −23.6529 0.9000 1.696800 55.52 10 37.1909 0.7644 11 21.65532.6218 1.808090 22.74 12 −149.6082 D12 (Variable) *13 31.4469 1.49311.589130 61.15 *14 −454.8143 D14 (Variable) 15 ∞ 1.7118 (Stop) 1617.8093 0.9000 1.834000 37.18 17 10.8731 2.4554 1.497820 82.57 18−36.9740 1.5005 19 14.0517 2.3992 1.518230 58.82 20 −15.0205 1.00341.851350 40.13 *21 −25.0875 0.2985 22 23.6629 2.4328 1.902650 35.73 238.6520 D23 (Variable) 24 −29.8985 2.0872 1.617720 49.81 25 −17.6129 BFImage ∞ surface [Aspherical surface data] The 6th surface κ = 1.00000 A4= 1.30134E−05 A6 = 5.20059E−08 A8 = −1.38176E−09 A10 = 6.06866E−12 A12 =0.00000E+00 The 13th surface κ = 0.3322 A4 = 5.55970E−05 A6 =3.96498E−07 A8 = 3.97804E−09 A10 = 0.00000E+00 A12 = 0.00000E+00 The14th surface κ = 4.0000 A4 = 9.44678E−05 A6 = 5.47705E−07 A8 =1.37698E−23 A10 = 0.00000E+00 A12 = 0.00000E+00 The 21th surface κ =−1.0412 A4 = 8.07840E−06 A6 = −1.60525E−07 A8 = −3.84486E−09 A10 =0.00000E+00 A12 = 0.00000E+00 W M T [Various data] Zoom ratio 4.71 f10.29845 32.00216 48.49978 FNO 3.60 5.06 5.79 ω 39.76047 13.631739.16599 Y 8.00 8.00 8.00 φ 7.80 8.30 8.30 TL 79.34243 95.80944 105.57918BF 13.25602 13.25602 13.25602 [Variable distance data] f 10.2984532.00216 48.49978 D5 1.80000 16.93666 22.35926 D12 18.49692 5.540521.80069 D14 3.61695 3.90524 5.82908 D23 5.42688 19.42534 25.58847[Amount of movement of focusing group upon focusing] Distance between1.00 m 1.00 m 1.00 m object and image Amount of movement 0.2652 0.74811.2334 [Lens group data] Group Group first Group focal number surfacelength G1 1 57.25524 G2 6 −11.09964 G3 13 49.98341 G4 15 28.96589 G5 2465.16201 [Values corresponding to conditional expressions] Conditionalexpression(1)f3/ft = 1.031 Conditional expression(2)(−f2)/fw = 1.078Conditional expression(3)f3/f4 = 1.726 Conditional expression(4)ν3 =61.15 Conditional expression(5)(d3t − d3w)/fw = 0.215 Conditionalexpression(6)f4/ft = 0.597 Conditional expression(7)fR/fw = 6.326Conditional expression(8)f3/ft = 1.031 Conditional expression(9)(d3t −d3w)/fw = 0.215 Conditional expression(10)fR/fw = 6.326 Conditionalexpression(11)(−f2)/fw = 1.078 Conditional expression(12)f4/ft = 0.597Conditional expression(13)(d1t − d1w)/ft = 0.424 Conditionalexpression(14)(d2w − d2t)/ft = 0.344 Conditional expression(15)f3/ft =1.031 Conditional expression(16)f4/ft = 0.597 Conditionalexpression(17)fR/fw = 6.326 Conditional expression(18)(−f2)/fw = 1.078Conditional expression(19)(d3t − d3w)/fw = 0.215 Conditionalexpression(20)f3/ft = 1.031 Conditional expression(21)f4/fw = 2.812Conditional expression(22)f3/f4 = 1.726 Conditionalexpression(23)(−f2)/ft = 0.229 Conditional expression(24)f1/ft = 1.180Conditional expression(25)fR/fw = 6.326

Based on Table 1, it is found that in the zoom optical system ZL1according to the present example, the conditional expressions (1) to(25) are satisfied.

FIGS. 2A, 2B, and 2C illustrate graphs showing various aberrations(spherical aberration, astigmatism, distortion, coma aberration, andlateral chromatic aberration) upon focusing on infinity regarding thezoom optical system ZL1 according to Example 1, where FIG. 2A depicts awide-angle end state, FIG. 2B depicts an intermediate focal lengthstate, and FIG. 2C depicts a telephoto end state. FIGS. 3A, 3B, and 3Cillustrate graphs showing various aberrations (spherical aberration,astigmatism, distortion, coma aberration, and lateral chromaticaberration) upon focusing on a short-distance object (1.00 m of adistance between the object and image) regarding the zoom optical systemZL1 according to Example 1, where FIG. 3A depicts a wide-angle endstate, FIG. 3B depicts an intermediate focal length state, and FIG. 3Cdepicts a telephoto end state. FIGS. 4A, 4B, and 4C illustrate graphsshowing meridional lateral aberration when correcting image blur uponfocusing on infinity regarding the zoom optical system ZL1 according toExample 1 (shift amount of a vibration-free lens group=0.1 mm), whereFIG. 4A depicts a wide-angle end state, FIG. 4B depicts an intermediatefocal length state, and FIG. 4C depicts a telephoto end state. In thepresent example, optical performance when controlling vibration, asillustrated in FIGS. 4A, 4B and 4C, is illustrated in a meridionallateral aberration diagram corresponding to a screen center and an imageheight ±5.6 mm of an image height.

In each graph showing aberrations, FNO means a F number, and NA meansthe number of an aperture of light emitted from the lens arrangedclosest to the image, A means an angle of incidence of light, that is, ahalf angle of view (units: degree), H0 means the height of the object(units: mm), and Y means an image height. d means d-line, and g meansg-line. What is not described with d or g means an aberration accordingto d-line. In graphs showing spherical aberration, a solid lineindicates spherical aberration. In graphs showing astigmatism, a solidline indicates a sagittal image surface and a dashed-line shows ameridional image surface. In graphs showing coma aberration, a solidline indicates coma aberration in a meridional direction. Note that alsoin graphs showing aberrations of each example described below, the samesigns are used as those in the present example.

As obvious based on each graph showing aberrations illustrated in FIGS.2A, 2B and 2C, FIGS. 3A, 3B and 3C, and FIGS. 4A, 4B and 4C, in the zoomoptical system ZL1 according to Example 1, various aberrations areappropriately corrected covering a range of from a wide-angle end stateto a telephoto end state, therefore high optical performance can beobtained. It is found that high image-forming performance can beobtained upon correcting image blur.

EXAMPLE 2

Example 2 is described using FIG. 5, FIGS. 6A, 6B and 6C, FIGS. 7A, 7Band 7C, FIGS. 8A, 8B and 8C and Table 2. The zoom optical system ZL(ZL2) according to Example 2 comprises, as illustrated in FIG. 5, inorder from an object along an optical axis, a first lens group G1 havingpositive refractive power, a second lens group G2 having negativerefractive power, a third lens group G3 having positive refractivepower, a fourth lens group G4 having positive refractive power, and afifth lens group G5 having positive refractive power. An aperture stop Sis provided between the third lens group G3 and the fourth lens groupG4, and the aperture stop S configures the fourth lens group G4. Thefifth lens group G5 is the lens group arranged closest to the image.

The first lens group G1 is composed of, in order from the object alongthe optical axis, a cemented lens composed of a negative meniscus lensL11 having a convex surface facing the object and a biconvex positivelens L12, and a positive meniscus lens L13 having a convex surfacefacing the object.

The second lens group G2 is composed of, in order from the object alongthe optical axis, a negative meniscus lens L21 having a convex surfacefacing the object, a negative meniscus lens L22 having a concave surfacefacing the object, and a biconvex positive lens L23. Note that thenegative meniscus lens L21 is a complexed aspherical lens made fromresin and glass, in which a lens surface on the object side isaspherical-shaped.

The third lens group G3 is composed of a positive meniscus lens L31having a convex surface facing the object. Note that the positivemeniscus lens L31 is a glass-molded aspherical lens in which a lenssurface on the object side is aspherical-shaped.

The fourth lens group G4 is composed of, in order from the object alongthe optical axis, a fourth A sublens group G4A configured of a cementedlens composed of a negative meniscus lens L41 having a convex surfacefacing the object and a biconvex positive lens L42, a cemented lenscomposed of a biconvex positive lens L43 and a negative meniscus lensL44 having a concave surface facing the object, and a fourth B sublensgroup G4B configured of a cemented lens composed of a negative meniscuslens L45 having a convex surface facing the object and a positivemeniscus lens L46 having a convex surface facing the object. Note thatthe negative meniscus lens L44 is a glass-molded aspherical lens, inwhich a lens surface on the image side is aspherical-shaped.

The fifth lens group G5 is composed of a positive meniscus lens L51having a concave surface facing the object.

In the zoom optical system ZL2 according to the present embodiment, thefirst lens group G1 to the fourth lens group G4 move along the opticalaxis so that an air distance between the first lens group G1 and thesecond lens group G2, an air distance between the second lens group G2and the third lens group G3, an air distance between the third lensgroup G3 and the fourth lens group G4, and an air distance between thefourth lens group G4 and the fifth lens group G5 respectively changeupon zooming. The fifth lens group G5 is fixed to the image surface I.

Specifically speaking, the first lens group G1, the third lens group G3,and the fourth lens group G4 move to the object side upon zooming from awide-angle end state to a telephoto end state. The second lens group G2moves to the image side from a wide-angle end state to an intermediatefocal length state, and moves to the object side from the intermediatefocal length state to a telephoto end state. The aperture stop S movesto the object side together with the fourth lens group G4.

With this arrangement, upon zooming, the air distance between the firstlens group G1 and the second lens group G2 increases, the air distancebetween the second lens group G2 and the third lens group decreases, theair distance between the third lens group G3 and the fourth lens groupG4 decreases from a wide-angle end state to an intermediate focal lengthstate and increases from the intermediate focal length state to atelephoto end state, and the air distance between the fourth lens groupG4 and the fifth lens group G5 increases. An air distance between theaperture stop S and the third lens group G3 decreases from a wide-angleend state to an intermediate focal length state, and increases from theintermediate focal length state to a telephoto end state.

Focusing is performed by moving the third lens group G3 along theoptical axis. Specifically speaking, the third lens group G3 is moved tothe image side along the optical axis upon focusing from an infinityobject to a short-distance object.

When image blur is generated, a correction of image blur(vibration-control) on the image surface I is performed by moving thefourth A sublens group G4A as a vibration-controlled lens group in amanner of having a component in a direction perpendicular to the opticalaxis.

Table 2illustrates values of each various data in Example 2. Surfacenumbers 1 to 26 in Table 2 correspond to each optical surface of ml tom26 illustrated in FIG. 5.

TABLE 2 [Lens Data] Surface number R D nd νd Object ∞ surface 1 144.94351.6000 1.846660 23.80 2 57.9139 4.6578 1.696800 55.52 3 −430.8049 0.10004 49.1887 3.5211 1.696800 55.52 5 158.0589 D5 (Variable) *6 504.46410.0800 1.560930 36.64 7 234.1101 1.0000 1.834810 42.73 8 9.4881 5.5305 9−17.0787 0.9276 1.741000 52.76 10 −1027.3916 1.0145 11 34.5727 2.68351.808090 22.74 12 −53.1261 D12 (Variable) *13 24.3966 1.6530 1.58887061.13 14 296.0192 D14 (Variable) 15 ∞ 1.5000 (Stop) 16 17.3960 0.90001.883000 40.66 17 11.0000 2.8505 1.497820 82.57 18 −48.0307 1.5000 1912.4669 2.8380 1.487490 70.32 20 −14.1721 0.9000 1.851080 40.12 *21−35.5823 0.1000 22 19.0885 0.9000 1.883000 40.66 23 7.1245 1.87741.620040 36.40 24 8.9496 D24 (Variable) 25 −30.0000 3.6500 1.69680055.52 26 −19.7882 BF Image ∞ surface [Aspherical surface data] The 6thsurface κ = −1.9998 A4 = 2.80199E−05 A6 = −2.77907E−07 A8 = 2.24720E−09A10 = −8.56636E−12 A12 = 0.00000E+00 The 13th surface κ = 1.7623 A4 =−2.39838E−05 A6 = −7.89804E−08 A8 = 2.79454E−09 A10 = 0.00000E+00 A12 =0.00000E+00 The 21th surface κ = −0.1893 A4 = −9.56775E−06 A6 =−6.24519E−07 A8 = 1.01416E−08 A10 = 0.00000E+00 A12 = 0.00000E+00 W M T[Various data] Zoom ratio 6.59 f 10.29976 39.99987 67.89953 FNO 3.645.06 5.81 ω 39.73502 10.92213 6.56887 Y 8.00 8.00 8.00 φ 8.60 9.90 9.90TL 89.92002 109.96784 121.58326 BF 13.25085 13.25085 13.25085 [Variabledistance data] f 10.29976 39.99987 67.89953 D5 1.80000 24.18110 32.41506D12 25.02141 7.23672 2.58202 D14 4.80996 3.66893 5.14775 D24 5.2539121.84636 28.40370 [Amount of movement of focusing group upon focusing]Distance between 1.00 m 1.00 m 1.00 m object and image Amount ofmovement 0.3072 0.9550 1.8445 [Lens group data] Group Group first Groupfocal number surface length G1 1 68.26199 G2 6 −12.46728 G3 13 45.04911G4 15 40.55521 G5 25 72.75019 [Values corresponding to conditionalexpressions] Conditional expression(1)f3/ft = 0.633 Conditionalexpression(2)(−f2)/fw = 1.210 Conditional expression(3)f3/f4 = 1.111Conditional expression(4)ν3 = 61.13 Conditional expression(5)(d3t −d3w)/fw = 0.033 Conditional expression(6)f4/ft = 0.597 Conditionalexpression(7)fR/fw = 7.063 Conditional expression(8)f3/ft = 0.663Conditional expression(9)(d3t − d3w)/fw = 0.033 Conditionalexpression(10)fR/fw = 7.063 Conditional expression(11)(−f2)/fw = 1.210Conditional expression(12)f4/ft = 0.597 Conditional expression(13)(d1t −d1w)/ft = 0.451 Conditional expression(14)(d2w − d2t)/ft = 0.330Conditional expression(15)f3/ft = 0.663 Conditional expression(16)f4/ft= 0.597 Conditional expression(17)fR/fw = 7.063 Conditionalexpression(18)(−f2)/fw = 1.210 Conditional expression(19)(d3t − d3w)/fw= 0.033 Conditional expression(20)f3/ft = 0.663 Conditionalexpression(21)f4/fw = 3.937 Conditional expression(22)f3/f4 = 1.111Conditional expression(23)(−f2)/ft = 0.184 Conditionalexpression(24)f1/ft = 1.005 Conditional expression(25)fR/fw = 7.063

Table 2 shows that in the zoom optical system ZL2 according to thepresent embodiment the conditional expressions (1) to (25) aresatisfied.

FIGS. 6A, 6B and 6C illustrate graphs showing various aberrations uponfocusing on infinity regarding the zoom optical system ZL2 according toExample 2 (spherical aberration, astigmatism, distortion, comaaberration, and lateral chromatic aberration), and FIG. 6A depicts awide-angle end state, FIG. 6B depicts an intermediate focal lengthstate, and, FIG. 6C depicts a telephoto end state. FIGS. 7A, 7B and 7Cillustrate graphs showing various aberrations (spherical aberration,astigmatism, distortion, coma aberration, and lateral chromaticaberration) upon focusing on a short distance object regarding the zoomoptical system ZL2 according to Example 2 (1.00 m of distance betweenthe object and image) where FIG. 7A depicts a wide-angle end state, FIG.7B depicts an intermediate focal length state, and FIG. 7C depicts atelephoto end state. FIGS. 8A, 8B, and 8C illustrate graphs showingmeridional lateral aberration when correcting image blur upon focusingon infinity regarding the zoom optical system ZL2 according to Example 2(shift amount of a vibration-free lens group=0.1 mm), where FIG. 8Adepicts a wide-angle end state, FIG. 8B depicts an intermediate focallength state, and FIG. 8C depicts a telephoto end state. In the presentexample optical performance when controlling vibration, as illustratedin FIGS. 8A, 8B and 8C, is illustrated in a meridional lateralaberration diagram corresponding to a screen center and ±5.6 mm of animage height.

As obvious based on each graph showing aberrations illustrated in FIGS.6A, 6B and 6C, FIGS. 7A, 7B and 7C, and FIGS. 8A, 8B and 8C, in the zoomoptical system ZL2 according to Example 2, various aberrations areappropriately corrected covering a range from a wide-angle end state toa telephoto end state, and a range from an infinity focusing state to ashort-distance focusing state, therefore high optical performance can beobtained. It is found that high image-forming performance can beobtained when correcting image blur.

EXAMPLE 3

Example 3 is described using FIG. 9, FIGS. 10A, 10B and 10C, FIGS. 11A,11B and 11C, FIGS. 12A, 12B and 12C and Table 3. The zoom optical systemZL (ZL3) according to Example 3 comprises, as illustrated in FIG. 9, inorder from an object along an optical axis, a first lens group G1 havingpositive refractive power, a second lens group G2 having negativerefractive power, a third lens group G3 having positive refractivepower, a fourth lens group G4 having positive refractive power, a fifthlens group G5 having negative refractive power, and a sixth lens groupG6 having positive refractive power. An aperture stop S is providedbetween the third lens group G3 and the fourth lens group G4, and theaperture stop S configures the fourth lens group G4. The sixth lensgroup G6 is the lens group arranged closest to the image.

The first lens group G1 is composed of, in order from the optical axis acemented lens composed of a negative meniscus lens L11 having a convexsurface facing the object and a biconvex positive lens L12, and apositive meniscus lens L13 having a convex surface facing the object.

The second lens group G2 is composed of, in order from the object alongoptical axis, a negative meniscus lens L21 having a convex surfacefacing the object, a biconcave negative lens L22, and a positivemeniscus lens L23 having a convex surface facing the object. Note thatthe negative lens L22 is a glass-molded aspherical lens in which a lenssurface on the object side is aspherical-shaped.

The third lens group G3 is composed of a biconvex positive lens L31.Note that the positive lens L31 is a glass-molded aspherical lens inwhich the lens surface on the object side is aspherical-shaped.

The fourth lens group G4 is composed of, in order from the object alongthe optical axis, a fourth A sublens group G4A configured of a cementedlens composed of a negative meniscus lens L41 having a convex surfacefacing the object and a biconvex positive lens L42, and a fourth Bsublens group G4B configured of a cemented lens composed of a biconvexpositive lens L43 and a negative meniscus lens L44 having a concavesurface facing the object. Note that the negative meniscus lens L44 is aglass-molded aspherical lens in which the lens surface arranged on theimage side is aspherical-shaped.

The fifth lens group G5 is composed of a negative meniscus lens L51having a convex surface facing the object.

The sixth lens group G6 is composed of a positive meniscus lens L61having a concave surface facing the object.

In the zoom optical system ZL3 according to the present example, thefirst lens group G1 to the fifth lens group G5 move along the opticalaxis upon zooming so that an air distance between the first lens groupG1 and the second lens group G2, an air distance between the second lensgroup G2 and the third lens group G3, an air distance between the thirdlens group G3 and the fourth lens group G4, an air distance between thefourth lens group G4 and the fifth lens group G5, and an air distancebetween the fifth lens group G5 and the sixth lens group G6 respectivelychange. The sixth lens group G6 is fixed to the image surface I.

Specifically speaking, the first lens group G1, the third lens group G3,the fourth lens group G4, and the fifth lens group G5 move to the objectside upon zooming from a wide-angle end state to a telephoto end state.The second lens group G2 moves to the image side from a wide-angle endstate to an intermediate focal length state, and moves to the objectside from the intermediate focal length state to a telephoto end state.The aperture stop S moves to the object side together with the fourthlens group G4.

With this arrangement, upon zooming, the air distance between the firstlens group G1 and the second lens group G2 increases, the air distancebetween the second lens group G2 and the third lens group decreases, andthe air distance between the third lens group and the fourth lens groupG4 decreases from a wide-angle end state to an intermediate focal lengthstate, and increases from the intermediate focal length state to atelephoto end state, the air distance between the fourth lens group G4and the fifth lens group G5 increases, and the air distance between thefifth lens group G5 and the sixth lens group G6 increases. The airdistance between the aperture stop S and the third lens group G3decreases from a wide-angle end state to an intermediate focal lengthstate, and increases from the intermediate focal length state to atelephoto end state.

Focusing is performed by moving the third lens group G3 along theoptical axis. Specifically speaking, this is performed by moving thethird lens group G3 to the image side along the optical axis uponfocusing from an infinity object to a short-distance object.

When image blur is generated, a correction of image blur(vibration-controlled) on the image surface I is performed by moving thefourth A sub lens group G4A as a vibration-free lens group in a mannerof having a component in the direction perpendicular to the opticalaxis.

Table 3 shows values of each data in Example 3. Surface numbers 1 to 24in Table 3 correspond to each optical surface of ml to m24 illustratedin FIG. 9.

TABLE 3 [Lens Data] Surface number R D nd νd Object ∞ surface 1 270.76981.6000 1.84666 23.80 2 63.2289 4.7857 1.58913 61.22 3 −180.7756 0.1000 438.2772 3.3872 1.69680 55.52 5 162.5542 D5 (Variable) 6 222.4687 0.90001.72916 54.61 7 8.6817 5.3065 *8 −19.5238 0.9000 1.69680 55.52 9 33.57660.1038 10 19.7682 2.5354 1.84666 23.80 11 434.3570 D11 (Variable) *1226.1871 1.7281 1.58887 61.13 13 −76.6701 D13 (Variable) 14 ∞ 1.7051(Stop) 15 16.6153 0.9002 1.83400 37.18 16 9.9827 2.6157 1.49782 82.57 17−36.7432 1.5000 18 16.2913 2.2592 1.51823 58.82 19 −17.2434 0.90001.85108 40.12 *20 −31.3248 D20 (Variable) 21 28.0868 0.9000 1.9026535.72 22 9.2493 D22 (Variable) 23 −37.3758 2.2000 1.61772 49.81 24−18.1325 BF Image ∞ surface [Aspherical surface data] The 8th surface κ= 1.0000 A4 = 2.09316E−05 A6 = −8.10797E−07 A8 = 2.75349E−08 A10 =−4.70299E−10 A12 = 2.62880E−12 The 12th surface κ = 1.0000 A4 =−4.37334E−05 A6 = 3.04727E−07 A8 = −6.38106E−09 A10 = 0.00000E+00 A12 =0.00000E+00 The 20th surface κ = 1.0000 A4 = 2.28740E−05 A6 =−3.19205E−07 A8 = −1.46715E−10 A10 = 0.00000E+00 A12 = 0.00000E+00 W M T[Various data] Zoom ratio 4.71 f 10.30000 32.00000 48.51858 FNO 3.535.00 5.72 ω 39.75617 13.57625 9.11928 Y 8.00 8.00 8.00 φ 8.20 8.80 8.80TL 80.36557 92.30690 103.19342 BF 13.30097 13.30097 13.30097 [Variabledistance data] f 10.30000 32.00000 48.51858 D5 1.80638 15.63570 22.37678D11 18.74841 4.51318 2.11693 D13 5.83635 4.73970 5.51292 D20 1.500003.72584 3.97118 D22 4.84649 16.06454 21.58766 [Amount of movement offocusing group upon focusing] Distance between 1.00 m 1.00 m 1.00 mobject and image Amount of movement 0.1896 0.4064 0.6618 [Lens groupdata] Group Group first Group focal number surface length G1 1 60.91787G2 6 −9.90833 G3 12 33.35587 G4 14 15.48045 G5 21 −15.63253 G6 2354.62879 [Values corresponding to conditional expressions] Conditionalexpression(1)f3/ft = 0.687 Conditional expression(2)(−f2)/fw = 0.962Conditional expression(3)f3/f4 = 2.155 Conditional expression(4)ν3 =61.13 Conditional expression(5)(d3t − d3w)/fw = 0.031 Conditionalexpression(6)f4/ft = 0.597 Conditional expression(7)fR/fw = 5.304Conditional expression(8)f3/ft = 0.687 Conditional expression(9)(d3t −d3w)/fw = −0.031 Conditional expression(10)fR/fw = 5.304 Conditionalexpression(11)(−f2)/fw = 0.962 Conditional expression(13)(d1t − d1w)/ft= 0.424 Conditional expression(14)(d2w − d2t)/ft = 0.343 Conditionalexpression(15)f3/ft = 0.687 Conditional expression(17)fR/fw = 5.304Conditional expression(18)(−f2)/fw = 0.962 Conditionalexpression(19)(d3t − d3w)/fw = −0.031 Conditional expression(20)f3/ft =0.687 Conditional expression(21)f4/fw = 1.503 Conditionalexpression(22)f3/f4 = 2.155 Conditional expression(23) (−f2)/ft = 0.204Conditional expression(24)f1/ft = 1.256 Conditional expression(25)fR/fw= 5.304

Base on Table 3, it is found that in the zoom optical system ZL3according to the present embodiment, the conditional expressions (1) to(11), (13) to (15), and (17) to (25) are satisfied.

FIGS.10A, 10B and 10C illustrate graphs showing various aberrations(spherical aberration, astigmatism, distortion, coma aberration, andlateral chromatic aberration) upon focusing on infinity regarding thezoom optical system ZL3 according to Example 3, where FIG. 10A depicts awide-angle end state, FIG. 10B depicts an intermediate focal lengthstate, and FIG. 10C depicts a telephoto end state. FIGS.11A, 11B and 11Cillustrate graphs showing various aberrations (spherical aberration,astigmatism, distortion, coma aberration, and lateral chromaticaberration) upon focusing on a short-distance object regarding the zoomoptical system ZL3 according to Example 3 (1.00 m of distance betweenthe object and image), where FIG. 11A depicts a wide-angle end state,FIG. 11B depicts an intermediate focal length state, and FIG. 11Cdepicts a telephoto end state. FIGS. 12A, 12B, and 12C illustrate graphsshowing meridional lateral aberration when correcting image blur uponfocusing on infinity regarding the zoom optical system ZL3 according toExample 3 (shift amount of the vibration-free lens group=0.1 mm), whereFIG. 12A depicts a wide-angle end state, FIG. 12B depicts anintermediate focal length state, and FIG. 12C depicts a telephoto endstate. In the present example, optical performance when controllingvibration, as illustrated in FIGS. 12A, 12 B and 12C, is illustrated ina meridional lateral aberration diagram corresponding to a screen centerand an image height ±5.6 mm.

As found based on each graph showing aberrations illustrated in FIGS.10A, 10B and 10C, FIGS.11A, 11B and 11C, and FIGS. 12A, 12B and 12C, inthe zoom optical system ZL3 according to Example 3, various aberrationsare appropriately corrected covering a range of from a wide-angle endstate to a telephoto end state, and a range from an infinity focusingstate to a short-distance object, therefore high optical performance canbe obtained. It is found that high image-forming performance can beobtained upon correcting image blur.

EXAMPLE 4

Example 4 is described using FIG. 13, FIGS. 14A, 14B and 14C, FIGS. 15A,15B and 15C, FIGS. 16A, 16B and 16C and Table 4. The zoom optical systemZL (ZL4) according to Example 4 comprises, as illustrated in FIG. 13, inorder from an object along an optical axis, a first lens group G1 havingpositive refractive power, a second lens group G2 having negativerefractive power, a third lens group G3 having positive refractivepower, and a fourth lens group G4 having positive refractive power. Anaperture stop S is provided between the third lens group and the fourthlens group G4, and the aperture stop S configures the fourth lens groupG4. The fourth lens group G4 is the lens group arranged closest to theimage.

The first lens group G1 is composed of, in order from the object alongthe optical axis, a cemented lens composed of a negative meniscus lensL11 having a convex surface facing the object and a positive meniscuslens L12 having a convex surface facing the object, and a positivemeniscus lens L13 having a convex surface to the object side.

The second lens group G2 is composed of, in order from the object alongthe optical axis, a biconcave negative lens L21, a biconcave lensnegative lens L22, and a cemented lens composed of a biconvex positivelens L23 and a biconcave negative lens L24. Note that the negative lensL22 is a glass-molded aspherical lens in which the lens surface on theobject side is aspherical-shaped.

The third lens group G3 is composed of a positive meniscus lens L31having a convex surface facing the object. Note that the positivemeniscus lens L31 is a glass-molded aspherical lens in which the lenssurface on the object side is aspherical-shaped.

The fourth lens group G4 is composed of, in order from the object sidealong the optical axis, a fourth A sublens group G4A configured of acemented lens composed of a negative meniscus lens L41 having a convexsurface facing the object and a biconvex positive lens L42, a cementedlens composed of a biconvex positive lens L43 and a biconcave negativelens L44, and a fourth B sublens group G4B configured of a biconvexpositive lens L45. Note that the negative lens L44 is a glass-moldedaspherical lens in which the lens surface on the image side isaspherical-shaped.

In zoom optical system ZL4 according to the present example, the firstlens group G1 to the fourth lens group G4 move along the optical axisupon zooming so that an air distance between the first lens group G1 andthe second lens group G2, an air distance between the second lens groupG2 and the third lens group G3, and an air distance between the thirdlens group G3 and the fourth lens group G4 respectively change.

Specifically speaking, the first lens group G1 to the fourth lens groupG4 move to the object side upon zooming from a wide-angle end state to atelephoto end state. The aperture stop S moves to the object sidetogether with the fourth lens group G4.

With this arrangement, upon zooming, the air distance between the firstlens group G1 and the second lens group G2 increases, the air distancebetween the second lens group G2 and the third lens group decreases, andthe air distance between the third lens group and the fourth lens groupG4 decreases from a wide-angle end state to an intermediate focal lengthstate, and increases from the intermediate focal length state to atelephoto end state. An air distance between the aperture stop S and thethird lens group G3 decreases from a wide-angle end state to anintermediate focal length state, and increases from the intermediatefocal length state to a telephoto end state.

Focusing is performed by moving the third lens group G3 to the opticalaxis along the optical axis. Specifically speaking, this is performed bymoving the third lens group G3 to the image side along the optical axisupon focusing from an infinity object to a short-distance object.

When image blur is generated, a correction of image blur(vibration-controlled) on the image surface I is performed by moving thefourth A sublens group G4A as a vibration-free lens group in a manner ofhaving a component in a direction perpendicular to the optical axis.

Table 4 below shows values of each data in Example 4. Surface numbers 1to 23 in Table 4 correspond to each optical surface of ml to m23illustrated in FIG. 13.

TABLE 4 [Lens Data] Surface number R D nd νd Object ∞ surface 1 77.50971.0000 1.75520 27.57 2 36.9718 5.6271 1.58913 61.22 3 167.7984 0.1000 442.4933 4.6381 1.69680 55.52 5 206.8356 D5 (Variable) 6 −873.2108 1.00001.77250 49.62 7 7.8543 3.6373 *8 −26.1695 1.0000 1.69680 55.52 9 27.74050.5875 10 15.7767 2.7220 1.75520 27.57 11 −33.7553 0.6000 1.79500 45.3112 131.6242 D12 (Variable) *13 16.5456 1.4427 1.58887 61.13 14 214.1576D14 (Variable) 15 ∞ 1.8000 (Stop) 16 10.9743 1.0000 1.80440 39.61 176.8392 2.4312 1.49782 82.57 18 −31.7167 1.8000 19 12.8502 1.7243 1.5168063.88 20 −34.8585 2.1512 1.85108 40.12 *21 10.5402 5.0997 22 17.82162.0000 1.54814 45.51 23 −380.5160 BF Image ∞ surface [Aspherical surfacedata] The 8th surface κ = 1.0000 A4 = 9.05226E−06 A6 = −3.64342E−07 A8 =1.64340E−08 A10 = −2.40084E−10 A12 = 2.62880E−12 The 13th surface κ =1.0000 A4 = −3.32881E−05 A6 = −5.73267E−07 A8 = 1.34421E−08 A10 =0.00000E+00 A12 = 0.00000E+00 The 21th surface κ = 1.0000 A4 =4.36460E−05 A6 = −1.73977E−06 A8 = −8.65204E−08 A10 = 4.98963E−09 A12 =0.00000E+00 W M T [Various data] Zoom ratio 4.71 f 10.30000 35.0000048.50000 FNO 3.65 5.61 5.72 ω 43.22847 12.93946 9.34123 Y 8.00 8.00 8.00φ 7.50 7.50 7.50 TL 75.14938 98.84478 107.15583 BF 13.51683 29.9677530.85637 [Variable distance data] f 10.30000 35.00000 48.50000 D52.09904 21.23006 29.53997 D12 14.54727 2.99470 1.80000 D14 4.625224.29125 4.59848 [Amount of movement of focusing group upon focusing]Distance between 1.00 m 1.00 m 1.00 m object and image Amount ofmovement 0.1532 0.4169 0.7343 [Lens group data] Group Group first Groupfocal number surface length G1 1 67.90812 G2 6 −9.06196 G3 13 30.36765G4 15 27.85994 [Values corresponding to conditional expressions]Conditional expression(20)f3/ft = 0.626 Conditional expression(21)f4/fw= 2.705 Conditional expression(22)f3/f4 = 1.090 Conditionalexpression(23)(−f2)/ft = 0.187 Conditional expression(24)f1/ft = 1.400

Based on Table 4, it is found that in the zoom optical system ZL4according to the present embodiment the conditional expressions (20) to(24) are satisfied.

FIGS. 14A, 14B and 14C illustrate graphs showing various aberrations(spherical aberration, astigmatism, distortion, coma aberration, andlateral chromatic aberration) upon focusing on infinity regarding thezoom optical system ZL4 according to Example 4, where FIG. 14A depicts awide-angle end state, FIG. 14B depicts an intermediate focal lengthstate, and FIG. 14C depicts a telephoto end state. FIGS. 15A, 15B and15C illustrate graphs showing various aberrations (spherical aberration,astigmatism, distortion, coma aberration, and lateral chromaticaberration) upon focusing on a short-distance object regarding the zoomoptical system ZL4 according to Example 4 (1.00 m of distance betweenthe object and image), where FIG. 15A depicts a wide-angle end state,FIG. 15B depicts an intermediate focal length state, and FIG. 15C showsa telephoto end state. FIGS. 16A, 16B, and 16C illustrate graphs showingmeridional lateral aberration when correcting image blur upon focusingon infinity regarding the zoom optical system ZL4 according to Example 4(shift amount of a vibration-free lens group=0.1 mm), where FIG. 16Adepicts a wide-angle end state, FIG. 16B depicts an intermediate focallength state, and FIG. 16C depicts a telephoto end state. In the presentexample optical performance when controlling vibration, as illustratedin FIGS. 16A, 16B and 16C, is illustrated in a meridional lateralaberration diagram corresponding to a screen center and an image height±5.6 mm.

As found based on each graph showing aberrations illustrated in FIGS.14A, 14B and 14C, FIGS. 15A, 15B and 15C, and FIGS. 16A, 16B and 16C, inthe zoom optical system ZL4 according to Example 4, various aberrationsare appropriately corrected covering a range of from a wide-angle endstate to a telephoto end state, and a range from an infinity focusingstate to a short-distance focusing state, therefore high opticalperformance can be obtained. It is found that high image-formingperformance can be obtained upon correcting image blur.

According to each example above, it is possible to realize the zoomoptical system in which the focusing lens group is small, and which hashigh optical performance upon zooming and focusing.

According to each example above, it is possible to realize the zoomoptical system having high optical performance over a whole zoom range.

According to each example above, it is possible to realize the zoomoptical system having high optical performance also when correctingimage blur.

In order to make the present invention understandable, the descriptionswere made with elements of the embodiments, however, needless to say,the present invention is not limited to the above. The followingcontents can be suitably adopted within a range which does not spoil theoptical performance of the zoom optical system of the presentapplication.

Although as examples of values of the zoom optical system ZL accordingto the first to fourth embodiments, four groups, five groups, and sixgroup configurations are exampled, however they are not limited to thoseconfigurations, therefore another group configuration (for instance,seven groups, etc.) can be adopted. Specifically speaking, this isapplicable to a configuration in which a lens or a lens group is addedclosest to the object, or a configuration in which a lens or a lensgroup is added closest to the image. Note that a lens group means partwhich has at least one lens separated with an air distance which changesupon zooming.

In the zoom optical systems ZL according to the first to fourthembodiments, in order to perform focusing from an infinity object to ashort-distance object, it is appreciated that part of lens group, awhole one lens group, or a plurality of lens groups is configured tomove in the optical axis direction as a focusing lens group. Although inthe present embodiment the third lens group G3 is exampled as a focusinglens group, however, at least part of the second lens group G2, at leastpart of the third lens group G3, at least part of the fourth lens groupG4, or at least part of the fifth lens group G5 can be configured as thefocusing lens group. This focusing lens groups are applicable toautofocus, and suitable for driving by a electromotor for the autofocus(for instance, an ultrasonic motor, etc.).

In the zoom optical systems ZL according to the first to fourthembodiments, although the fourth A sublens group G4A is exampled as aconfiguration in which image blur generated due to camera shake, etc. iscorrected by moving any one of a whole lens group or partial lens groupas a vibration-free lens group in a manner of having a component in thedirection perpendicular to the optical axis, or rotating and moving(swinging) them in an inner surface direction including the opticalaxis, this is not limited as above, for example, at least part of thethird lens group G3, at least part of the fourth lens group G4, or atleast part of the fifth lens group G5 may be configured of thevibration-free lens group.

In the zoom optical systems ZL according to the first to fourthembodiments, a lens surface may be configured of a spherical surface ora plane, or configured of an aspherical surface. In case that a lenssurface is a spherical surface or a plane, it is possible to easily havelens processing and an assembly adjustment, and to prevent degradationof optical performance due to errors of the processing and the assemblyadjustment, thus it is preferable. It is preferable because there isless degradation of depiction performance when an image surface isshifted. In case that a lens surface is an aspherical surface, theaspherical surface may be formed as any one of an aspherical surfacewhich is formed through grinding processing, a glass mold asphericalsurface which glass is formed into an aspherical surface configurationusing a mold, and a complexed aspherical surface which resin is formedon a surface of glass into an aspherical surface configuration. It isappreciated that a lens surface is formed as a diffractive surface,additionally a lens is formed as a graded-index lens (GRIN lens) or aplastic lens.

In the zoom optical systems ZL according to the first to fourthembodiments, it is preferable that the aperture stop S is disposed inthe fourth lens group G4, or in its vicinity. Note that it isappreciated that instead of providing a member as an aperture stop, therole is substituted with a frame of the lens.

In the zoom optical systems ZL according to the first to fourthembodiments, an antireflection film having high transmittivity in alarge wavelength band may be applied to each lens surface in order toreduce flare and ghost and attain high optical performance with highcontrast.

EXPLANATION OF NUMERALS AND CHARACTERS

ZL (ZL1-ZL4) Zoom optical system

G1 First lens group

G2 Second lens group

G3 Third lens group

G4 Fourth lens group

G4A Fourth A sublens group

G4B Fourth B sublens group

G5 Fifth lens group

G6 Sixth lens group

S Aperture stop

I Image surface

1 Camera (Optical device)

1-49. (canceled)
 50. A zoom optical system comprising, in order from anobject along an optical axis, a first lens group having positiverefractive power, a second lens group having negative refractive power,a third lens group having positive refractive power, and a fourth lensgroup having positive refractive power, a distance between the firstlens group and the second lens group, a distance between the second lensgroup and the third lens group, and a distance between the third lensgroup and the fourth lens group changing upon zooming, and the fourthlens group comprising, in order from the object along the optical axis,a fourth A sublens group that is movable with a movement component in adirection perpendicular to the optical axis in order to correct imageblur, and a fourth B sublens group.
 51. A zoom optical system accordingto claim 50, wherein the following conditional expression is satisfied:0.480<f3/ft<4.000 where ft denotes a focal length of the zoom opticalsystem in a telephoto end state, and f3 denotes a focal length of thethird lens group.
 52. A zoom optical system according to claim 50,wherein the fourth A sublens group has positive refractive power.
 53. Azoom optical system according to claim 50, wherein the followingconditional expression is satisfied:0.900<f4/fw<4.450 where fw denotes a focal length of the zoom opticalsystem in a wide-angle end state, and f4 denotes a focal length of thefourth lens group.
 54. A zoom optical system according to claim 50,wherein the following conditional expression is satisfied:0.600<f3/f4 <4.000 where f3 denotes a focal length of the third lensgroup, and f4 denotes a focal length of the fourth lens group.
 55. Azoom optical system according to claim 50, wherein the followingconditional expression is satisfied:0.155<(−f2)/ft<0.500 where ft denotes a focal length of the zoom opticalsystem in a telephoto end state, and f2 denotes a focal length of thesecond lens group.
 56. A zoom optical system according to claim 50,wherein the following conditional expression is satisfied:0.750<f1/ft<3.000 where ft denotes a focal length of the zoom opticalsystem in a telephoto end state, and f1 denotes a focal length of thefirst lens group.
 57. A zoom optical system according to claim 50,further comprising a fifth lens group disposed to an image side of thefourth lens group along the optical axis, wherein a distance between thefourth lens group and the fifth lens group changes upon zooming.
 58. Azoom optical system according to claim 50, wherein a lens group arrangedclosest to the image is fixed relative to an image surface upon zooming.59. A zoom optical system according to claim 50, wherein a lens grouparranged closest to an image has positive refractive power.
 60. A zoomoptical system according to claim 50, wherein the following conditionalexpression is satisfied:3.000<fR/fw<9.500 where fw denotes a focal length of the zoom opticalsystem in a wide-angle end state, and fR denotes a focal length of alens group arranged closest to an image.
 61. A zoom optical systemaccording to claim 50, wherein only the third lens group moves along theoptical axis upon focusing.
 62. A zoom optical system according to claim50, wherein the third lens group moves toward an image upon focusingfrom e-infinity object to a short-distance object.
 63. A zoom opticalsystem according to claim 50, wherein the first lens group moves towardthe object upon zooming from a wide-angle end state to a telephoto endstate.
 64. A zoom optical system according to claim 50, wherein thedistance between the first lens group and the second lens groupincreases upon zooming from a wide-angle end state to a telephoto endstate.
 65. A zoom optical system according to claim 50, wherein thedistance between the second lens group and the third lens groupdecreases upon zooming from a wide-angle end state to a telephoto endstate.
 66. A zoom optical system according to claim 50, wherein thefourth lens group comprises an aperture stop.
 67. A zoom optical systemaccording to claim 50, wherein an aperture stop is disposed between thethird lens group and the fourth lens group.
 68. An optical deviceequipped with the zoom optical system according to claim
 50. 69. Amethod for manufacturing a zoom optical system comprising, disposing, inorder from an object along an optical axis, a first lens group havingpositive refractive power, a second lens group having negativerefractive power, a third lens group having positive refractive power,and a fourth lens group having positive refractive power, each lensbeing arranged in a lens-barrel such that a distance between the firstlens group and the second lens group, a distance between the second lensgroup and the third lens group, and a distance between the third lensgroup and the fourth lens group change upon zooming, the fourth lensgroup comprising, in order from the object along the optical axis, afourth A sublens group that is movable with a movement component in adirection perpendicular to the optical axis in order to correct imageblur, and a fourth B sublens group.